For finding content on Netflix, use Instantwatcher - it's not fancy but way, way better for finding what's new/interesting on Neftlix than the Netflix site.
My impression is that there's a good bit of overlap between Netflix and Amazon Prime, but Netflix is overall better suited to my tastes. YMMV. If you do prime, though, you get the benefit of free 2-day shipping on all your Amazon orders as well (though that's a slippery slope... when I had it, I found myself buying more stuff and also never shopping locally, which I felt bad about).
Netflix is plenty for a light tv/movie watcher like my family (probably watch an hour or two one or two nights a week, plus a kid's show once or twice a week). I have a few shows I like that have plenty of seasons on Netflix (Breaking Bad, Mad Men, Sherlock, Arrested Development, Firefly, etc.), so since I only watch an episode or two a week there's plenty available for me. When I want to see a recent movie, I just rent it on demand from Amazon for $3 or $4 (no need to subscribe for that). If you tend to watch a lot of tv or movies, though, you'll run through the good content on Netflix pretty quick.