I do remember when I had my first couple of 25s, I wanted to do ALL the tamers with what I had, but it doesn't quite work that way.
You have your Idol at 25. That's a great start! The Idol is a powerful all-rounder, my personal favourite general go-to pet. It will almost solo many of the Pandaren tamers, and it will provide a levelling prop for lower level pets in wild battles.
However, it won't do everything
, and no one pet added with it will allow it to do everything. The game is designed so that you need many different kinds of pet in different situations.
Go to http://www.wow-petguide.com/
and click around around the strategies there, looking for [pet]Anubisath Idol[/pet]. Many or most of the tamers can be beaten by an Idol and maybe another, for example: http://www.wow-petguide.com/index.php?m=3&s=32&a=2
There are also many other ways to beat tamers not listed there; those are just the most sure, most straightforward strategies. So other pets can also work.
So with that as context, let's try your questions:
Adrenalin wrote:1. boosting a low level pet, which means the team basically just consists of two pets,
you mean boosting a low level pet in wild battles. The Idol will do this nicely all on its own, but other pets will do it more quickly, depending on what wild pets you're battling. For example, if you're wild battling in Mistfall, you're mostly facing Aquatics, so you would want a Flyer for the fastest battles.
For wild levelling, I like pets that can heal themselves, for fewest trips to the Stable Master.
Against Critters (in Halfhill) the fastest and smoothest wild levelling comes from a cat with Devour. [pet]Cornish Rex Cat[/pet] with Pounce, Screech, Devour is my personal favourite. Many people will prefer [pet]Feline Familiar[/pet]. My view is that the Cornish Rex is ideally specialised for critters, but the Familiar is more useful in other types of battles as well. Either way, your strategy with cats is never to kill your opponent except with Devour. You should get that heal on every kill, even if it means delaying the kill by one round.
Another excellent wild killer of Critters is [pet]Teroclaw Hatchling[/pet]. For a new battler, this might be an easy purchase. Teroclaws are very very cheap, and they are very powerful pets - top-tier in PvP - with a lot of other uses. Against Critters, you will use the Teroclaw with Claw, Dodge and Ravage, and you will make a point of never killing except with Ravage. If Aquatics are mixed in, as at Halfhill, you might take Alpha Strike instead of Claw in the first slot.
I've tested Cats vs Teroclaw, and Cats are a little faster and definitely smoother against critters, but the Teroclaw is everywhere, cheap, already Blue, and has hundreds of other uses.
Against Aquatics (in Mistfall) I like the [pet]Pterrordax Hatchling[/pet], but it isn't much used elsewhere.
Adrenalin wrote:2. defeating level 25 trainers and
As I say, go to http://www.wow-petguide.com/
and look around.
From a recent analysis of my own teams that I did, here are my other top pets for the tamers:
[pet]Mechanical Pandaren Dragonling[/pet]
[pet]Emerald Proto-Whelp[/pet] P/P breed
[pet]Emperor Crab[/pet] P/P breed
[pet]Nexus Whelpling[/pet] P/P breed
[pet]Zandalari Anklerender[/pet] P/P or P/B breed
Adrenalin wrote:3. defeating bosses.
[pet]Pandaren Water Spirit[/pet]
This pair do what is called "Howlbomb", which will pretty much take down any "boss" pet like the Beasts of Fable or the Tanaan pets.
If you had every pet I recommended here as a Blue 25, you could easily finish most content in Pandaria and Draenor (no, not the Celestial Tournament, but that one takes a bit of work.)