The absolute best is VSL's new Imperial grand - 100 velocity layers per note (!). It's the closest thing to playing a real piano. It's also the first library with sympathetic resonance samples. Unfortunately you only get a Bosendorfer with this library, but it sounds incredible.
Next is EWQL's piano library, which has some issues with sampling - there's a lot of strange sub-bass (HVAC system/passing truck?) on some pp notes in the middle of the keyboard in the Steinway lib. That's probably not a huge problem to most people, but it drives me nuts. This library is a better value compared to VSL - you get Steinway, Bosendorfer, Bechstein, and Yamaha samples....and it's quite a lot cheaper than VSL.
Synthology Ivory is another option, but I'm not too crazy about the sound. It seems like they nuked the samples with noise reduction.
You mentioned that you're looking for something similar to Pianoteq, but better - well, unfortunately samples are the only way to go, which are not lightweight and not cheap like a softsynth. Also, in order to get the most out of any piano VSTi, it HAS to be played by a human. You just can't program convincing piano, IMHO. Anyway, just take that into consideration before you drop a ton of money on something and wonder why it sounds so mechanical...unless that's what you're going for.
