Not counting taking advantage of the companion trick (lame).

For my sword & shield Nord:

I use Heavy Armor training from Farkas as I really dislike how you can’t level this skill without actually getting hit... even worse for Light Armor users IMO...

I sometimes use Block training from Nia Strongarm...

Sometimes Smithing from Eorland...

I’ll probably use Alchemy training on my next assassin... better than grinding potions...

On that note, trainers are so much better than “grinding” IMO...

I never use trainers. I do it all on my own.

Pretty much the same as you. I use them for the slower leveling skills, like Heavy/Light Armor, Block, and Restoration.

I actually usually don't use trainers, even though I couldn't tell you why. I don't have anything against trainers really. Actually, I may have just thought of a reason. I don't like buying things that I could get out in the field training. I guess that means I could train my alchemy/smithing/enchanting then, but still.

I use it for just about everything but combat skills like one handed. I do for magic a lot, especially restoration.

I use them to level passive skills, like light armor or heavy armor. I also use them for smithing (that's how I go to 90 smithing) and a bit of enchanting.

Same here. Add Destruction to that.

The crafting skills are so easy to level anyway, I think, plus a good source of income.

Anything that I don't use enough to advance at an acceptable rate yet want developed to obtain a particular perk or spell. Since I don't train or grind skills, only use them, I find myself needing to supplement the advancement of desirable but lesser used skills through trainers.

I use a trainer for a secondary Skill that is covered by another Skill. If I have a character who uses Bows for a Ranged Skill, I will train Destruction. I almost always train Restoration from level 10 to 20 because of the Perks that become available, like Respite, increased Magicka Regeneration, and Necromage.

I always train up Pickpocket, even though I never use it. I figure some day I will.

All the other skills increase as they need to as I play the game, so no need to train them.

Heavy armor, one handed, block, alteration (for the magic resistance) and destruction (for elemental augmentations).