I like them both.
A single game in Revolution can be played in an evening - because it was designed from the ground up to play that way.
I suppose it's possible to complete a game of Civ 4 in one evening - but it wasn't really designed from the ground up for that purpose. Myself, whenever I launch a new game of Civ4 , it's rarely the case that I'll finish that campaign within a week. More often than not I never even finish at all - life gets in the way, and then I have to leave the game, and when I do come back, days, or even weeks later, I'll have forgotten what I was doing. Then, usually, I'll start a campaign anew. I'm not saying it's not a great experience, because it is - it's just that you'll need quite a bit of time on your hands.
I've got to admit though, that there's something to be said for being able to complete a game like this in just one sitting. Note that a game of Revolution will still take you hours though. (Trust me, it won't feel like hours - you'll wonder where the time went.)
Actually, you know what, I'm going to go out on a limb here and say go with Revolution. The truth is you can't really go wrong in doing this. Once you begin to understand the dynamics of the game (this takes just two or three games to do) you'll be hooked. And when I say hooked, I mean hooked.
Revolution, I believe, is one of those games that actually causes a chemical reaction to take place in your brain - how else can I describe the sense of euphoria that I will often feel after playing for a couple of hours straight? Also, don't worry about the controller issue. It's not even an issue. It's a fantastic setup. I'm a keyboard man myself - but this game was MEANT for a controller. It just feels right.
And if by some weird circumstance you actually dislike Revolution then you can give it to one of your friends and make their summer - I can assure you that it wouldn't be difficult finding somebody who will love this game with a passion.
(EDIT: Also, if you do buy Revolution first, then what's stopping you from buying CIV 4 for you computer after that? My guess is that if you play and get to know Revolution, then a few months from now you'll be dying to get your hands on the pc version, just to see how it plays in comparison.)