I suppose there's a lot of different categories you could work out a Top 5 for- favourite ships in the show, how well the models are done, how well they look like they're supposed to, etc etc
I'm just gonna base mine on simply how I like looking at the models on my desk (granted I don't have them all)
It's a tough choice, and I'd be leaving out some great ones, but in no particular order...
1. NX-01 – for the reasons I gave earlier
2. Enterprise-B – Sorry Exceslior fans, don't hate me, but I do prefer the refit look. Only got it a couple of weeks ago but I'm loving this model.
3. Enterprise-E – I think ever since I first caught a glimpse of this ship in the First Contact trailer I wanted a model of this ship, and it took me 18 years to get one

4. Delta Flyer – Again, a new addition but its just so cool and sleek looking, love it
5. Romulan Warbird – originally I only intended on purchasing the Starfleet ships, and this was the first Alien one I got. To actually hold it in your hand and see it from different angles and dimensions, and just how much space there is in the "gap" really makes me appreciate the ship more. Great model.
Honourable mentions- 2152 BOP, Enterprise-D, Vor'cha.
As for the Reliant- it's a great model, but I've never had it on display properly. Is it just mine or does it not fit in the holder properly
at all? The slightest knock to the table and it will fall out, giving me a heart attack that the nacelles will break off. So back in the box it's gone. Actually the Romulan Warbird had a similar problem too.