Going to go ahead and do all the remaining animals at once. It's not like each of them is going to be thoroughly debated in the main thread.
Large size, decent physical stats, aaaaaand there's the 8 RHD. Another for the -0 pile. Even its sole special ability doesn't function properly: rather than increase or double your charge damage, it sets it to a fixed amount, thereby eliminating what was probably the last viable strategy at this level.
A decent swim speed and a bite attack, as well as a quite situational aquatic scent ability and some blindsense. I suspect being a normal character and taking a shark as your companion would be better in every way. -0 LA for these.
It's large, yes, but it's also very pricy (7 RHD). -0 LA.
I'm having dragon purgatory flashbacks. -0 LA.
3 RHD, medium size, okay stats, decent bite attack, and low speeds in three movement modes. Predictably, there's an improved grab and a constrict ability, which I guess is still semi-usable at ECL 3, but I'll go with -0 for now.
Snake, Giant Constrictor
MORE animals with additional HD and little other change. In case you were wondering, the extra HD did not redeem this thing, so -0 LA it is.
Snake, Tiny Viper
Surprisingly interesting. Sure, the speed sucks, but 1d6 constitution damage is surprisingly potent for an at-will ECL 1 poison, Weapon Finesse for free is always nice, and the three movement modes are still useful as well. Barely worth +0 LA, mostly because of some niche uses.
Snake, Small Viper
Basically a straight upgrade from the tiny viper, so +0 LA once more.
Snake, Medium Viper
2 RHD? Not going to cut it when the main selling point is 'bite attack that deals more than one damage, sometimes'.
Snake, Large Viper
Surprisingly enough, these may actually be better than the medium ones. I know, I was surprised too, but a size upgrade and +2 strength may actually be worth the extra HD. Still -0 LA though.
Snake, Huge Viper
Either you are reading this because I just posted this and you read through all of it, or because you're actually considering playing an unintelligent limbless serpent with 6 RHD. I'd point out that they deserve -0 LA, but I feel like if you're here you're not the person to care about optimization anyways.
A larger octopus with another HD, slightly better stats (though intelligence went down), a higher jet speed, and the removed ability to move around on land. The grapple bonuses are neat, but the extra HD tips this over the -0 LA threshold in my opinion.
12 RHD? I'm not even sure I need to say this is -0 LA, but here it is anyway.
Lion with bigger numbers and one additional RHD? I'll allow it. +0 LA.
The toad, only notable for being invisible to peasants when sitting straight in front of them on a twillit flat plain while surrounded by candles. Other than a great Hide bonus (which is still worse than a hairy spider's), there is literally no reason to play a toad. -0 LA.
Tiny, with free Weapon Finesse, a dexterity bonus, a climb speed, a weak bite attack, and an Attach ability that's so incredibly weak I'm not sure how the developers expected it to be used (seriously, even against foes with only 2 HP it's risky to use). -0 LA.
12 RHD? No, just no. 'Big aquatic air-breathing meatshield' is such an incredibly narrow role that I just can't imagine a campaign where a character like this would be relevant.
Oh hey, a baleen whale with a bite attack. Still -0 LA.
The best of the whales, though that's more because of their lower HD than any kind of inherent ability. -0 LA.
You could be a riding dog and literally have something that looks like a wolf, acts like a wolf, and plays like a wolf, but has superior stats in nearly any way. -0 LA.
Obligatory: a persisted Monstrous Regeneration spell.
Basically a dire badger with some minor things switched around. Sure, that'll earn ya +0 LA.