Ok as we know one of the best additions in Skyrim compared to previous elder scroll games is that you have a huge variety of followers from whom you can chose.But what you usually do is hire one follower at the begining and continue together raising levels.Now ive reached a point where i am a bit bored of him but still all other followers are at a very low level and they probably are going to get killed instantly in a tough battle.I want to "test" as many followers as i can in battle but i dont want to end up killing them all.

Do you know about the Wabbajack trick?

I stand open to correction but i thought they levelled up to your level at the point you acquire them and then do not increase?

no they level with you. Here's a link, where you can see which followers go to the highest level....there are many who go to at least lvl 50, thats high enough surely?

http://www.uesp.net/wiki/Skyrim:Followers

Followers are way too annoying to bring anywhere. They either shoot you in the back or step in front of your melee swings. They set off traps you've carefully bypassed, run ahead and aggro extra mobs or do so little damage and have so few hit points that you're constantly baby-sitting them. Other than as portable storage, I don't get why anyone would want them.