In my estimation, it is in same segment (it is high end). It has oracle based encrypted vault, good scalabliity and is designed as an "enterprise wide" solution.
How they compare specifically feature for feature, I cannot say (no direct experience with the others).
Product center has plenty of horsepower to meet all of ones needs. It's robust, pretty well behaved and has a slew of "additional" capabilities and extensions (cad add ons, workflow, bom configurator) as well as a wide range of standard configuration abilities.
Our implementation here is fairly plain vanilla (not too customized).
I can attest to the ProductCenter vs. SmarTeam comparison first-hand, having replaced SmarTeam in our company with ProductCenter. ProductCenter doesnt have all the fancy functionality that SmarTeam has "out-of-the-box", but our experience was that the majority of that "functionality" that SmarTeam liked to talk about was either rarely needed or took heavy custom coding to "adapt" it to our environment. ProductCenter concentrates on core functionality while still providing a full-featured API for customization. Having been down both roads, I much prefer the ProductCenter route.
In response to SMA's synopsis, I would upgrade his reliability grade to very good, the key being a solid hardware platform. The cost difference between ProductCenter and SmarTeam for our implementation amounted to a difference of ~$2000. I would also agree that the support is awesome.