If you can fly SkyTeam airlines (NW, DL, CO) from where you live, you should definitely go for one of their programs - two reasons. 1) the qualification for Platinum is only 75,000 miles...one of the lowest levels out there and 2) the programs actually give good benefits - I have been upgraded from coach to first on every flight in the last two years with only a couple of exceptions on really busy days. With other programs, getting upgraded usually requires certificates.

That said, award availability on SkyTeam, especially NW and DL is very limited - but getting upgraded most of the time really makes up for it.