What followers should I gear up first?

[Mamut]

Slowly Im getting more and more followers to lvl 99/100 and I wonder now what makes follower good and which one should I gear up first? Are there any abilities more usefull than others? How to determine if folower is good or crap? I did not focus much on garrison and I dont have much experience and i dont wanna waste epic upgrades on crap follower :/

[Kuthe]

No follower is 'crap' as they quest more they level from green to blue to purple, and at purple they get 2 abilities.
Honestly at the start, probably gear up Millhouse, Leeroy or Croman if you have them, because they're all instan-epics (purple) and have 2 abilities each.
Create a list and work out how many of each spell you have, try to make it so they're remotely even. I currently have 3 of each + Nat sitting in my fishing thing. Resting at 25 capped followers.

It's not that stressful, you'll get your extra gear pieces over time, especially quicker if you run heroics as a tank/healer and get a bag, have a salvage hut, or have a war mill, all help, and you'll build them up over time.

[Thelxi]

I'd gear up any 3 epic ones, all with different abilities. Don't gear up followers with the same abilities at first, you want a good spread of counters.

[ThePants999]

Check which counters are required for the Highmaul missions. Focus on followers that will counter two things in one mission.

[JemiS]

It can also be worth gearing up a few rates that you're leveling to epic- some of the really good +exp missions have 615 requirements, and can be great for fast leveling on your targeted alts, but only if they're geared enough.

[Zurine]

It's worth noting that you may want to save some items rather than use them immediately. For example, wait until you get an armor or weapon set (these are automatic 615, 630, etc. weapons and armor) before using an item enhancement (+3, +6, +9) on that follower. This is overall a more efficient way of using follower items, but it does require some patience as the sets are less common than the enhancements.

[Everwake]

Check which counters are required for the Highmaul missions. Focus on followers that will counter two things in one mission.

Exactly.

Go to Wowhead and look at all 4 Highmaul raid missions. Map the abilities out on a piece of paper and look for the counters amongst your followers. Try to level up the followers that have two counters to these missions.