Legion Family tamers, when their World Quests are up, are infinitely repeatable, so you can get more-or-less the same XP as Squirt from them. And every day, it is pretty sure that at least one of them is up. It's not quite as good as a permanent Squirt, because some of them are slower, and you will need bandages instead of having the heal beside you, but it's close. And it's all the time.
And because at least one of these tamers is pretty much always available, you can pig out on pet week with the Squirt-level XP times 3, every day of every pet week. I see Sir Galveston is up in both NA and EU right now, according to Wowhead. (Hm, thats pretty rare. Wonder if Wowhead have that right.)
Nyari suggested this order of speed/easiness for levelling: Squirt > Odrogg > Galveston > Bodhi > Tiffany > Robert > Andurs > Xorvasc > Grixis > Jarrun > Amalia > Aulier > Varenne > Merayl > Bredda but I'm sure you will have your own preferences. I levelled a dozen or so new-ish pets with Odrogg in about a quarter of an hour last pet week. And that with 3X XP is available every pet week, as well as every week with regular Tamer XP - no more waiting for SuperSquirt a couple of times a year!
https://wow-petguide.com/ has any strats you might need for them.