I was kinda thinking that if I start with the state-of-the-art RTS, in Starcraft 2, then what are the chances I'll be able to go back to the older RTS's and enjoy them at all?
If I start with something older, I can enjoy that game as much as I might have when it was new (considering I'm pretty much a complete and total RTS noob, though not at all a gaming noob). Then I can gradually advance with the newer RTS's as they presented new ideas, new flashier graphics, new ways to make the games less cumbersome, etc. Plus, that'll be MORE total gaming for me too, if I can spend time playing/enjoying the older games.
That all depends on the time you have to spend on gaming and if you prefer SP over MP...
If you have lots of free time and you prefer SP -> go for the old games!
personally i have just enough time to keep up with ~1-2 games, especially when trying to compete in MP matches!
So i want to play the "best" game available/the game that most of my friends play... atm for me this is SC2, followed with civ5 in a few weeks. by the time when these two games are getting boring/outaded there are a lot of new good games on the way (e.g. diablo 3 and the sc2 addons).
I prefer to play MP games with my friends, playing SP mostly as a "training" for MP matches... So playing an OLD game which none of my friends plays, feels like wasted time for me.