I just got a 19" Sony G420. I would've gotten a 17" LCD if I could've afforded it though. I'd definitely pick a 19" screen over a 15" LCD. 15" just isn't enough desktop space IMO.
I always thought that there was a much bigger difference between a 15" and 17", than a 17" or 19" display. I guess that pretty much goes for all the other screen sizes too. 21" isn't that big enough of jump over the 19" to make it worthwhile for me either. Neither is the difference from 14" to 15".
I guess what I'm trying to say is that 17" is the sweet spot. If you are going with a CRT, why not go with a 19" because the price difference is hardly anything. If you are going with a LCD, I would definitely spring for a 17".
.02¢
Sal