I've Played Civilization 3 for years (and just started getting into it again). Should I update to 4 or 5?

I love civ 3 and have played it on and off since it came out. It's pretty buggy on my new computer and I'm considering updating to a newer game. I've read a lot of reviews and am still undecided about switching to either 4 or 5. I figure [/r/games](/r/games) probably has some great advice.