When we play Space Crusade, my brother always picks the Blood Angels, because he likes the fighting style. He's also pretty good at it, because he usually devastates the opposition with relative little losses. In fact, he's a bit annoyed to have to lug around a Heavy Weapon, which is basically the laughing stock of his squad. Actually, when the "Out of ammo" chance card pops up, he usually begs / taunts me to remove his Rocket Launcher and replace it by a regular bolter as he feels that would actually make his Space Marine stronger instead of weaker. Which is usually the reason I skip him and take out a Heavy Weapon on either of the two other squads

The reason I see people turn down the Blood Angels so readily is because of the way they combat: in melee for the most part. The deeper reason is that in any melee combat, a Space Marine has the risk of dieing himself, rather than the alien being attacked - a risk you don't have when shooting at an alien instead. However, when I see how my brother plays it ... "Close Assault Blades" allow a diagonal attack, which requires enemies to roll 1 die less and "Bolt Pistols" which grant an addition white die during melee give a significant advantage over the enemy. Gretchins can't defend at all and Orcs and Chaos Marines are reduced to 1 white die vs. the Blood Angels' 3. The only real threats are the Androids and Dreadnoughts, but he usually moves his Admiral into position for those. The Admiral is a heavy hitter in melee in his own right and with an AV of 3 is pretty hard to hit in return. Against Dreadnoughts, going all out with a Melta Bomb usually makes quick work of those and in a hairy situation, "Blind Grenades" prevents most damage for that one turn.
Update: Did some math. When two units attack eachother in melee and one rolls 3 white vs. 1 white of the other, the odds are as follows:
13.58% chance the one with the single white combat die wins
28.09% chance the fight ends in a draw with neither combatant dieing
58.33% chance the one with the three white combat dice wins
The Blood Angel Space Marine has more than four times as much chance to kill his opponent than the other way around. And if you look at survival rate, the Blood Angel Space Marine survives 86.42% of the melee engagements, whereas the opponent only has 41.67% chance to be left standing after combat has finished.
Furthermore, since Space Marines with a Bolter only yield 5 points for the Chaos Player, Space Marines with a Heavy Weapon are usually more interesting targets and any losses are usually easily paid for - easier than for the Ultramarines or Imperial Fists. And even beyond that, usually the best way to take down Space Marines as the Chaos Player is to melee the Space Marines with your Orcs and Gretchin - where the Blood Angels excel over the other two squads and are therefore better shot down than engaged in melee.
Thoughts?
Also, with regards to the Ultramarines, to us they always feel like a bit of a "Jack of All Trades", which can also be summed up as "Master of None". In my group, it's actually considered the weakest squad; it doesn't specialize in anything and therefore doesn't have any real strengths. Is that just our perception?