If anyone has tried these three, which one might you recommend? I thought I might give redhat a go, but don't want to download all the ISO's over a 56k modem if it sucks !

Well, are you a complete Linux Newbie, or an are you a hard corps Linux geekster?

I am assuming (from the question) that you are pretty close to the newbie side. In which case comes the next question:
Are you coming over from Winbloze or are you fresh, untainted meat?

And I am assuming the first (that you are winbloze crossover) in which case I would suggest Mandrake. It's just enough like winbloze that you won't feel like you are in a new country all alone, but has the stability and usability of Linux. Further down the road after you have mastered the art of Linuxing you can move up to SuSe and eventually to Slackware.

I tried slack last week, but was still too advanced for me. Think I might move up to SuSe soon though.

Redhat I think is for the either the person brand new to computing or the business with 50+ users (to accomodate everyone that is a winbloze user at home).

I did the Redhat thing for about 2 weeks, just didn't have the feel that I need from a Linux OS. It seemed to want me to make everything Redhat. Like it's slogan is probably "If it's not Redhat then it's Sh*t." And I didn't like that too much.

Mandrake does that a little, but not very often. Usually you can install anything on there, even stuff built for Redhat. Not only that but it also makes it alot easier to download an ISO from it's website; Redhat made me do a little digging to find the mirrors for it's ISO's.

All in all, there is no easy short answer to your open ended question.

What are you going to use it for? What is your level of experience? What features can you not live without? And how cool do you want to sound when you tell everyone at school that you use a REAL OS?

hehe, don't need to sound cool at school, been working for a bit now :0. I've been using Linux for about 6 months, I've had mandrake 8.1 and currently have 8.2 on this laptop. I'll be using it mostly to write Java but my gf likes to play some games and surf the net. I'm not too bad with things, but I'm no sysadmin. I can get around though.
I'm running it on my laptop, and I just think things are a little funny now and then. It bugs me.

Little funny? Redhat probably won't solve your problems, I thought the same sort of thing. Actually I eventually worked out most of the problems, and those that I didn't these guys on this website did. So, just find a UI you are happy with, and go with it.