The Fusion 5 does not have a hardware decoder, but this is usually not necessary unless you have a slow computer. My brother is running his on an Athlon XP at 2.1GHz or so with a Radeon 9700 Pro. I think he has 768MB of RAM, and got a little stuttering before he remembered to turn on dual-channel memory.
I have the MyHD MDP-130 myself (plus the DVI daughtercard) and I love it. Very very low CPU usage (hardware decoder), QAM, everything you'd expect in a tuner. However, many will be put off by its rather high price. I think it's worth it if you want to spend the money though. But for "general" use, the Fusion 5 should be good. It supports QAM so you should get your local HD/digital channels over cable, as they're almost always sent unencrypted (you will not get premium/non-free channels like TNT-HD, ESPN-HD, HBO-HD, etc.).
Feel free to ask if you have any more specific questions about HDTV tuners, I tend to give a lot of people advice on them 😛
Edit: As long as you're getting a stable, solid signal, picture quality will be identical for all practical purposes. HDTV tuners are not like analog tuners in that they can vary in picture quality. The $99 Fusion 5 Lite will get you the same picture that my MyHD card does, assuming your computer is fast enough. DVICO has trial software and transport stream samples on their website that you can download to gauge the performance of HDTV playback on your computer; I would suggest downloading those just to make sure it'll run fine on your computer.
Edit 2: Read some of the previous posts and saw you were talking about analog NTSC picture quality too. 😛 From what I've seen of my brother's tuner, analog is fine on the Fusion.