The Vree are my favorite fleet by far. That said, most of the weaknesses of this fleet are also offset by using a swarm.
They have no clear-cut defenses like stealth, interceptors or shields (baring the Xarr and scouts of course). Likewise they have few advantages like a high hull or lots of damage/crew points. This makes the entire fleet look like a bunch of glass hammers. So, in order to make up for their obvious weaknesses, it is easy to swarm the enemy.
Now all that said, let us look at the hulls that I tend to rely on:
---The Best of the Vree---
Tzymm: this is a GREAT fighter. Just don't expect them to survive many dogfights.
Xarr: Oh Boy! This is THE strongest ship in the fleet. Although I think that the 2 for 1 patrol ships are better, this little guy will do quite a bit of damage for their simple Patrol designation. Also, this is one of your few hulls with something better than a 4!
Xixx: This is one of the few long range weapons out there so take at least one or 2. Unfortunately, they are very fragile, so don't expect them to do anything after they do their big volley.
Vaarl: This, IMO, is one of the best scouts out there! A good Stealth, a wicket weapon, +1 to scouting rolls (due to the Vree crew), in a Skirmish level vessel! One thing though, if the enemy is close enough for you to use your weapon, you are probably dead as this thing has about the same amount of Damage and Crew as some Patrol boats.
Xeel: This thing puts out some NASTY firepower and has access to 4 of our great fighter/bombers. What is NOT to like about it? Well, the hull 4 and average damage and crew are slightly holding it back. Also, if it only had Carrier 2 (hey, even a Carrier 1 would make this my favorite ship), then you could rest easily in offloading the fighters before it was blown to kingdom come. As shown in other threads, when taken in mass, this thing is to be feared for sure! Now the bad side: when the new book comes out, you can expect a solid loss in firepower. I'll still take it, only not as often.
---The Good---
Xill: Although I would obviously prefer 4 Xarr over a Xill, this thing has some decent guns. I find them to be a solid choice, and a great way to buy down when playing War and Battle level games, but I don't worry if I loose a Xill or 2 when playing a game (I can usually pull it out even when they die).
Xaak: I prefer the firepower and high hull over the Xill, it still only has a Raid level of damage and crew; making it VERY fragile. I guess if you want the command bonus, take it. Honestly, when I first saw this thing, I took it every time over the Xill, then I learned the trouble of that dreaded 4-6 critical and swore them off for good.
Xonn: Alright! So you loose 1 speed for 1 more hull (and damage and crew). You also get lots of extra dice. What's not to like about this thing... Well, it IS a little slow and it has no long range guns (unless you think that 15" is long range).
T'Zakk: I love this ship. That said, it tries to do too much for it to be a great ship (sorta like a War version of the Minbari's Neroon). If ONLY it had more damage and crew. IF ONLY it had another system of torpedoes (even if that means that each volley lost 1-2 AD). If ONLY it had more Tzymm and a carrier trait. As it stands, I think that it lacks a little oomph in one of those directions to make it a "great" ship.
Zorth: I have to say, this single fighter type is awesome! On it's own, you will not fear much from enemy fighters. Unfortunately, with all the good Anti-fighter traits in this particular fleet, you don't NEED this type of fighter unless going up against lots of range 3-4 fighter/ bombers. I tend to take a few of these guys so that I can tie up anyone who tries to take on the Tzymms. That said, you don't need them for every game.
---The not quite so Good---
Ximm: As a patrol level escort, this is sorta cool. Unfortunately, it is very fragile and you can do better with Zorths when taking on enemy fighters.
Vaarka: This would be a great ship except for the lowered stealth. Stick with the Vaarl, as the extra stealth is sorely needed.
Xirr and Xorr: This ship is just too fragile to take on much of anything. Stick with the Xixx if you insist on taking this model.
Overall, this is a great fleet for the League, but some races will chew you up:
Narn and Gaim: the abundance of E-mines will shatter your fighter swarms and crush most of you hull 4 ships (the majority of the fleet). Also, the Xarr, even though it has dodge and hull 5, will die quickly to double damage and triple damage E-mines.
Centauri: Swarms of Demos and Vorchans will crush most of your ships. With an Interceptors, and the ability to share them with other ships, you will be hurting for those early rounds of hurting the enemy with your torpedoes. Worse still they can out-range you and have the perfect weapons to lay waste to hull 4 ships (and double damage to boot). Your best bet is to "all power" past the front arc and hope that you survive the initial volley of firepower. Even then, it will be hard won.
There are some toughies, but the above 3 feel like you are fighting a serious, up-hill battle.