Just about everyone has their opinion about this, and I'm not sure there's a "wrong" answer. All personal preference. I personally own: Capture One (3 & 4), Lightroom (1 & 2), Canon DPP, BreezeBrowser, Bibble and RawShooter (not that it gets much use anymore).
I agree with your thoughts about Capture One 3.x versus Capture One 4. Though I have both, and used the 3.x for years as my main converter, it is long in the tooth as far as a few processing niceties, and C1-4 just seems clunkier.
I've moved on to Lightroom as my primary. I don't think it is the "sharpest" or "cleanest" RAW processor out there, but it has lots of flexibility. I also still like using Canon's DPP for some things. A while back I tried Silkipix. Not bad at all. A little quirky in the way it does things, but good results. I've had Bibble for years, but never really liked the results I got. I also tried DxO, but, honestly, with all the programs I already own, it didn't offer me something major the others didn't have. (I have heard, though, that it's quite good at pulling out the finest details.)
Almost every one of these programs is available in a 15- to 30-day full working demo. Download them. Select a handful of images that represent a wide-range of what you shoot, and see how they handle color, contrasty situations, over-exposure, under-exposure. The most important thing, aside from results, is how YOU like working with it and how quick and easy it is to pick up.