i wanna lick you rly badlyDepends what role I'm playing overall or what gearset I am currently using. If it was up to me I prefer to play the much more passive mid damage style of boomkin and push up very carefully with my team and run very little Hp for maximum mid pressure. This lends well to the troll racial which is what I have on my current only US boomkin and one of EU boomkins. I think the most attractive thing about tauren boomie isn't even the racial stun but the stam increase. The stun is vital for racial snowballing sometimes and is very good utility sure, but having 200 ish more hp (Because tauren gets 9 racial stamina and extra stamina from their actual base stats) is just really good when you're pugging.
So if you wanna be playing the utility boomkin go tauren (Tauren also better if you PuG a lot). Otherwise the troll racial is really powerful for mid pressure if you can deal with the lower health pool.
EDIT: Worth noting that though troll has the racial for damage it has really low base intellect alongside tauren (only 16). If faction is not a consideration then night elf is easily the best race for midfield druid (Unless you really value the tauren racial) because of the 4 more base intelect, very high base agility for cat form damage and shadowmeld being the most powerful alliance racial in the 19 bracket.
Not totally sure how the gear works out in 19 versus 29, but haste has serious diminishing returns after 30%ish when considering a fight consisting of lots of enemies.
goblin for the mobility