Wait for the steam summer sale in a few weeks, you’re likely to get Civ 4 complete (with expansions) for $10 and Civ 5 probably for $25 or less.
Civ 5 isn’t a total upgrade to Civ 4 - there are things Civ 4 does better. 5 is more streamlined and more accessible to new players, not sure how much experience you have with them. 4 has better city management, more stuff to keep an eye on, generally more strategy and planning. But it’ll be really hard to go back from 5 to 4, even if it does some things better, because the combat is so much better in 5.
I’d wait for the sale, grab both for cheap, and see which you like better.
Edit: For the post asking about Civ 3 - don’t bother, Civ 3 is possibly the worst of the civ games … relatively speaking, and not worth your time when you could get 4 which does pretty much everything better.
Huh. So far I like V more than IV, mostly for the combat, but having only very recently bought the latter I admit this is a superficial impression. What did you like more about IV (or what didn’t you like about V, if that’s more to the point)?
I feel that IV chugs along better than V and is more complete than V at this point. Perhaps in some time V will patch things up and get past IV, but for now, especially for someone who hasn’t played IV before, IV is a better place to be. V will always be there down the road. The two are different enough that one does not necessarily preclude the other. Might as well start with the cheaper one that has all the bugs squished.
If you can get the user-createdmods and scenarios to work on a Mac then Civ IV is the way to go. Some of the best - like the already mentioned Fall From Heaven II, are like totally new games. Personally I’m waiting for Civ V to come out in a complete or gold addition with all the Firaxis upgrades before I’ll move on to V.
Oh and I thought III was pretty good, except for the retarded corruption mechanic.
I bought civ 4 during the daily sale. I have it on disk somewhere but I haven’t played it for years. Going back to play it is hard - the squares, the crappy combat, the less streamlined interface… I acknowledge that some of the strategy and city management has more depth, and some of the mechanics are more interesting, but damn it’s hard to go back after you’ve been spoiled by the good parts of civ 5. I guess if you want to end up playing both, play civ 4 first so you don’t know what you’re missing yet.