If you like to tinker, I think the Profitec 600 is going to offer you the most flexibility (You can add flow control, manual prewetting/infusion, 58mm PF for accessories galore, etc).

However if you like more simplicity, the A53 is hard to beat. I've used the Mini Vivaldi II for over 10 years and recently having moved to an e61 machine, there are these small things about an e61 machine that can be maddening.

Both of them have great steaming capability, excellent temperature stability, and a long history of support (both vendor and online). Lastly, both can make excellent espresso, but you have a little bit control over some of the variables with the e61 machine.