I would say that it depends on your modeling skills and budget.
If you're not really experience with PE, then avoid White Ensign. Their stuff is beautiful, very fragile, but not suited to those with big fingers or clumsy tendencies. It's also pricey, but you get what you pay for.
Gold Medal is delicate, and mid-range in price. Their sets lack alot of the really super detail stuff the WEM frets carry.
Tom's is best suited for those with a limited budget looking to improve the ship without going insane while doing it. His sets are affordable, and provide the basic stuff you need to detail the model.
That's my opinion, I use all three companies on everything I do, sometimes, multiple parts from different frets on the same ship.
Jeff