I've played L5R since 1st ed, and frankly 2nd ed was the weakest version. If you've played 3rd ed, then 4th ed will be fairly familiar in terms of mechanics. I would prefer to play with 4th ed, though not everyone may have those books yet (it's not that long out). 3rd ed revised is possible, but I wouldn't play 2nd ed (It's too far back, I don't have the books, and didn't like it much anyway).
If you have the 3rd ed books, you can build a 4th ed character with some assistance from the GM.
I haven't played much 4th ed yet, but it did tidy a few things up from 3rd ed, and generally I like what I see of it.