In basic terms, Intel will do a lot more per Mhz. AMD might be able to throw out a 3.6Ghz 8 core CPU but it's not a lot of use in games that don't even fully utilise 4 cores yet. The FX-8150 is generally going to get beaten by a Sandy Bridge i3 in games.
In workstation based tasks, I believe both are viable. Those programs tend to make use of more cores which favours AMD. (Intel has Hyperthreading which kind of makes up for this if you go i3 or i7 though.) Just 'viable' isn't enough for me personally though, since AMD tend to use twice the power to get the job done. I'm a bit of a low noise freak.
The one place I would always go AMD is with their fusion APU's. Fantastic for laptops, HTPC's and very low end gaming machines. Intel's integrated graphics are a bit lacking at the moment, HD 4000 is the only one worth using for a balanced system in my opinion.