I'm wondering which one I should get. I've played a little bit of Fallout 3 for PC and I really enjoyed the mods. Are the New Vegas PC mods better? Should I spend my money on New Vegas for PC or Fallout 3 for PC?

Big mods develop and evolve over months and years... FO3 has been around for a while, meaning, there more, bigger and more mature mods for it.
But, there are already thousands of good mods for FNV and because the two are so similar and, mod-wise, FNV is a continuation of FO3, porting mods from one to the other is doable and lots of modders develop for both games.

So... I guess I'm not being very helpful, but both are great.

I would say go with FO3, because you can get the GOTY edition with ALL the DLC, and it also CURRENTLY, has more and better established Mods.

FO3 with just the DLC alone will keep you going a lot longer than FONV,
as long as you don't follow the main story, (which as is the norm for Bethesda,) is shorter than a book about
Physics Equations written by 'Lady Gaga'

I think you give Lady Gaga too much credit, but there are more and longer mods for FO3 than NV. That'll change as modders start making or porting mods into NV.

If you liked fallout 1&2, skip f3 and just start with new vegas

if youre getting for mods i agree that FO3 would probably serve you better. NV seems to be slower than FO3 in the modding area

Ok, cool, thanks guys