I recently purchased my first 58mm tamper.

I bought it from a company in Australia (coffeelab design) for what I thought was a decent price (compared to what was available locally here in Canada) which included the shipping to my door (about 10 days). It is a convex shape. What I like about it is the rubber grips. I have long fingers and the rubber grip around the piston keep my fingers from slipping down the base when I push down. Same goes for the rubber grip on the top keeping my palm from sliding around while holding it.