I'd say go for El Toro. Seeing as i just started on a patriot recreation.... but you could give it a try as well, im not trying to discourage you not to gove it a try.
Stealths tophat is really hard to get accurate. I managed it after about 2 weeks of working on the shaping, but i never released it because it isnt worth it as the ride is so short. Im also waiting to visit thorpe again myself and ride sealth so i can produce som 3ds for it, and then i may release it.
Anyway man, a really good Cobra rec is being done at Coaster Force, with 3ds, by Cobra, so i wouldnt do that. I would say stealth for you. Not that i dont think you are capable of the other rides, its just, i think you would have to have ridden the other coasters in the list already to recreate them accurately. Its like, im planning to recreate nemesis when my skills have reached a certain level that i think i can do it. Im not there yet. But i wouldnt even dream of recreating it if i hadnt ridden it, because the layout is so dfferent, you really need to know it well to get it right. I dont feel cpable of recreating it accurately yet, and ive ridden it over 50 times. If i were you, i would choose a ride you have ridden alot, and know the most about to recreate, as otherwise, your recreation wont be as accurate as possible. And seeing as you live in the UK, stealth seems the one you have the largest probability of riding.
EDIT: Yeah, but it was made in Nolimits Pro or something. It had a larger grid area.
I find recreations to much of a ***** to do only because I always find minor imperfections that aren't in the real coaster and then I just end up throwing it away as a result. That's just me though, but with that said I think patriot or toro would be cool.
Its not Nolimits as we know it, but Ole was involved and it looks pretty much the same as Nolimits apart from a few small differences, and what looks to be more advanced physics.
I'd try the Voyage, but you're probably screwed unless you know the exact terrain on HW! The Voyage simulation found on HW's site was actually made in NL, so you can refer to that.
I voted for Speed Monster and the least popular ride is the Cobra because I never heard of it. I choose Speed Monster because there are plenty of pictures but it just seems you don't really get a layout out of the pictures.