Does anyone have an opinion as to what method of filtration is best? I have a choice of using reverse osmosis or an EverPure filtration system.

I also had the choice and I chose reverse osmosis. It is completely natural, while everpure softens water via chemistry.
Anyway the topic was discussed many times on HB, try searching, you should find many posts.

You need to be careful with RO (Reverse Osmosis) water because if it is not post-treated, it is aggressive towards copper, aluminum, and brass. It sounds like this is for a plumbed-in machine, maybe your Portofino, and if you set up an RO system on the water line, you would want to post treat the water to balance it. This can be done a number of ways, with a mineral/brine balancing unit or with a blend of untreated water (usually less than 10%). It turns out to be a small chemistry experiment of sorts, but it is important because pure RO water will dissolve the copper from your machine over time.

When I worked in a chemical plant, I learned from the chemists that once RO water comes in contact with air (which it does when your boiler cools and the vacuum breaker valve releases), it immediately dissolves the carbon dioxide from the air, creating a mild solution of carbonic acid with a pH of around 5. This will not react with stainless steel, but it most definitely affects other metals. You wouldn't notice an immediate effect, and in fact it would start to descale your boiler, believe it or not, but over time it would cause the pump to lose efficiency and even wear away the tight seal on the steam valve among other parts. Espresso made with pure RO water also tastes a bit flat because there aren't enough minerals for the particles from the coffee to bind to.

I know EverPure cartridges can be expensive, but there are other DIY solutions. At our shop, we installed a salt-base ion-exchange water softener followed by a Big Blue carbon block filter and a 5 micron sediment filter, with a pressure regulator at the end and spit valves in between to relieve pressure when changing filters. The catch here is having the space and the willingness to invest in equipment on the front end, and some plumbing knowledge if you don't want to pay for install. If this is in your home, you can use the 20 inch Big Blue filters and set this up for your entire house.

Then again, this might be covered in many other posts you can search.

If your boiler has electronic refill, using a sensing rod for the internal water level, RO will overfill your boiler until it's coming out of the safety valve.

+1 for the mineralisation of RO water

There are a couple of things you need to ask first, along with reading Jim's Insanely Long Water FAQ. The first thing to ask is what your incoming water is like. If it's municipal water, you will be able to get a report from your utility that shows the range they've measured. If it's in the range of 50-100 ppm total hardness, and generally tastes good by itself, run it through carbon filtration and call it good. At the higher end of that, you'll have to descale once or twice a year. We're also assuming you're talking about a plumbed-in machine, since with a pour-over you can mix to get what you want. At higher levels of hardness, you will need some conditioning. But again, what you choose depends on how hard and what the water tastes like. As Ken Fox will be happy to tell you, he has hard water that otherwise tastes good, so he uses a small cation softener. I'm intrigued by the Next Filtration ScaleStop systems, for environments with maybe 100-300 ppm hardness, but I haven't actually installed one, so my intellectual fascination shouldn't count for much. As others have said, if you need an R/O system, you should definitely run a calcite cartridge after it to add a small amount of hardness back to the water.

Best,
David

although I always heard the same story of:
complete absence of minerals in water will not have enough voltage to trigger the autofill circuit ( I think it needs 2-3 volt ) when I called cigar some years ago to try to get an explanation directly from a producer of a specific possible affected component
I was also told that the sensitivity of the units is becoming less and less of an issue and also that some boxes have a potentiometer that can be adjusted to increase or decrease the sensitivity
now my own eyes experience,
I have several customers that own home units and use reverse osmosis,
some of 8-9 years old units and these particulars one in my own county ( which most of them share the same "source water")
some of this customer machines are prosumer middle grade units
every time I happen to open one of such boiler and look inside
I'm always impress of how clean they look and so far never saw a leak cause by The water treatment"
so my assumption
and I repeat that is an assumption
perhaps the source water to start with has a final result on how the RO water is then acting

now the taste bud factor is the other consideration
some customers puts mineral back in the tasteless water because they can taste the difference
some do not some use distilled water and cannot tell them apart from a shot with the highest mineral content water.

This thread on coffeed references an Illycafe paper on Water Quality for Espresso Coffee (article available for a fee) which talks about some of the effects of water hardness on espresso taste and flow rate. I didn't pay for the article but did find the coffeed thread interesting which pointed to difficulty at one location in getting the espresso dialed in because of the differences in water chemistry with soft water.

I have recently fitted an under-bench Ever Pure dedicated water filter system to my new Bezzera BZ40
Most coffee shops use them
Ever Pure brand with quick change head
This is fitted with a special coffee machine filter 2CB GW (Gourmet water filter for coffee applications)

The filter one uses can be very important

KK

Are you debating between RO and EverPure, or between a cation softener and EverPure? There's a difference.

A cation softener does not produce RO water. It removes only the hardness and not the alkalinity. Thus, if the untreated water has sufficient alkalinity, the water from the cation softener will not attack the metal of the machine. That said, if the untreated water has extremely high alkalinity, it will amplify the scaling effect of any residual hardness, and periodic descaling may be required (probably very infrequent like once or twice a year.) Residual hardness varies with the hardness of the input water and the effectiveness of the cation system. Our untreated water has hardness in the 130 ppm range and alkalinity in the 150 ppm range. My cation system has produced water with hardness in the 0-1 ppm range and no change in alkalinity (i.e., about 150 ppm) for the past four months without recharging. YMMV.

Also note that the hardness in the steam boiler can build up over time from the constant evaporation of the water. This can be ameliorated by using lots of hot water from the boiler or flushing it regularly, both of which will dilute its contents with fresh softened water. We use a lot of hot water here. Nevertheless, I drain the steam boiler monthly and test its water. So far, the hardness has risen only slightly, to the 1-2 ppm range. The alkalinity is a little higher, too, around 170 ppm. I suspect descaling won't be necessary for some time. Note that the coffee boiler is less subject to this sort of mineral concentration, partly because there's no deliberate evaporation and partly because fresh water flows into it every time you brew. Nonetheless, I drain my coffee boiler once a month, too. The water shows no concentration of minerals at all.

As for taste, I believe Jim Schulman has done some testing that indicates there's only a very slight flavor trade-off between using cation-softened water and water with ideal hardness for espresso. Presumably, the minerals that make up the alkalinity affect flavor, too. I doubt that I'm capable of tasting the difference, so I went with a cation system to reduce the need for descaling.

Don't use real RO (distilled water) in an espresso machine. It is likely to be slightly acidic, which will attack the metal over time, and the taste of the espresso will be decidedly inferior due to the complete lack of minerals.