Stealth exp from creatures roughly corresponds to combat level. Hiding at melee, attacking from hiding, poaching, and sniping will all teach stealth effectively, if your skill is challenged. If you are struggling to hide, try going without armor (shield only) or training discipline, as well as casting Earth Meld. Poaching at missile is easier than attacking at melee, and sniping is the hardest. So on a given creature, that may be a good progression - start by poaching, transition to attacking at melee and get the last few ranks by sniping.

In regards to creature recommendations, I tend to use the Elanthipedia hunting ladder as a very rough guide. https://elanthipedia.play.net/Category:Hunting_ladders

Assuming your combats trail your stealth slightly, perhaps elder brocket deer or warcats?

You can also stalk advance and hit a critter with a melee weapon. Rinse and repeat. You do have to actually do some damage with your weapon to reset the timer that's on the critter to learn well doing this. For me I usually start off by stalking and sniping whatever, then after I lock my bow I'll switch to a melee weapon to lock stealth.

Bluefalcon