Well, the purer the breed - S/S, P/P, H/H - the more raw stat points they get, so pure breeds are always interesting. But it's more about the moveset than the species.
Is an S/S [pet]Gilnean Raven[/pet] better than a B/B? For what purpose, exactly? In PvE, your flyer will almost always be faster than your opposition's non-flyer, so the extra speed is usually wasted. You probably want a Raven for CD, NS, AS until dead.
Let's say you survive 4 rounds, such that the S/S is faster for all 4, while the B/B is faster for 3.
S/S goes: 420 + 560 + 360 + 360 = 1700 damage
B/B goes: 444 + 592 + 370 + 222 = 1628 damage.
So the S/S does more damage. But if the B/B's extra 81 health means it gets in another round, that's another 222 damage, and the B/B wins. Or, if you have exactly 1000 HP to take down in two rounds, the B/B will do it but the S/S won't.
BUT, if you're using Peck instead of Alpha Strike, perhaps because your target has a shield, then the B/B wins in every scenario. The value of the stats depends on moveset rather than species. In the Raven case, Alpha Strike is better than Peck if you're faster - and if the target doesn't have a shield subtracting some damage from each attack.
I got a bit obsessively arithmetical about this when I was cleaning up my collection. With 13 species of rabbits and 22 snakes, you can afford to have lots of sub-optimal breeds in those movesets just for novelty. For the rest, though, I had to make choices.
I worked out, for each moveset, which was the breed I wanted, and went about getting that breed. Sometimes I wasn't sure, and got two or three breeds. Flyers are a problem, since Health translates into Speed. I had some fun during the event using my [pet]Flamering Moth[/pet] this week. People expect a moth to heal about as much as they expect the Spanish Inquisition.
I still don't know whether I prefer the H/S or the P/S breed. I suppose I could work out some scenario, but I'm lazy, and I still have 50 slots left.
S/S is quite specific. With these pets, you are sacrificing everything else to be faster, so there needs to be a move in the moveset that makes it pay off - a stun, a blind, a swap, or an extra hit if you're faster. If you're going to use [ability]Flurry[/ability], [ability]Crystal Prison[/ability], [ability]Blinding Poison[/ability], [ability]Alpha Strike[/ability], [ability]Blitz[/ability], or avoidances like [ability]Dodge[/ability], [ability]Lift-Off[/ability] or any other ability that removes you from attacks for a round, you want to be as fast as you can.
With S/S, you are probably aiming at PvP, because in PvE that speed likely won't pay off so well. Here are some notable pets I surely want in S/S [pet]Darkmoon Rabbit[/pet], [pet]Flayer Youngling[/pet], [pet]Death Adder Hatchling[/pet], [pet]Fiendish Imp[/pet], [pet]Alpine Foxling[/pet], [pet]Alpine Hare[/pet] or other fast rabbit, [pet]Crow[/pet], [pet]Bronze Whelpling[/pet], [pet]Frostfur Rat[/pet], [pet]Lil' Bad Wolf[/pet], [pet]Mechanical Scorpid[/pet], [pet]Nightshade Sproutling[/pet], [pet]Ore Eater[/pet], and on and on. Discodoggy has recently been starring an S/S [pet]Prairie Mouse[/pet] whose party trick is to use his speed for [ability]Survival[/ability].
For a different set of priorities, consider [pet]Junglebeak[/pet]. Even though the P/P breed has only 1339 health, you will probably be using it to include a [ability]Rain Dance[/ability] that will heal for 353, making the effective health almost 1700. You will also be getting your double-crit-chance 706 damage [ability]Nocturnal Strike[/ability] and a 353 damage [ability]Peck[/ability] out of its innings, and with any luck you can retire it to the back line then to fight another day.