All depends on what size fleets you think of using.
however the best ships for Narn
Patrol. nothing excels, personal choice, however you may want some for init sinks
Skirmish. Majority of peeps thing the Ka'Toc is the beens knees, it's certainly not far off, personally prefer the thentus, can't go wrong if you buy both, the other ships are less usefull
Raid, Var'Nic is one of the best raid ships in the game, and only a fool doesn't choose Dag'Kars. The T'Loth and G'Karith are decent, but not in the class of the other twp
Battle, well you have a G'QUan or varients, looks superb, less useful, but your only choice if you want anything at this level
War, take your pick, the Bin Tak is one of the finest warships in the game, the G'Vrahn is likewise. most people rate the G'Vrahn over the Bin Tak. I'd be happy with either, however the bin tak just looks cooler!
Armageddon. you can't get a model for this. If you get a proxy, it's a great ship.