Same as Blackwing, Helwyr's one - don't care much for the others. Mostly because I like Celtic themes/designs and that loosely fits the bill.
I wish/hope Jagex will one day decide to introduce a reasonably sized new location where such themes would work, something like the aesthetics of the lost grove or even the areas for Helwyr in GWD2; preferably the former over the latter as I just prefer the atmosphere more. Maybe somewhere based on the otherworld and the aos sí to give some variation to the game than just elves and only elves - hell.. they could maybe twist it into an elder god type thing lorewise.
Actually, I forgot all about it cresbot isn't too bad either (if only it could override legendary pets). Another thing I'd love to see is Jagex give followers, pets etc. more personality (unique or bland) to them rather than just the default stand there and ultimately do nothing.
Something like run animations for those it would be appropriate for IE. boss pets where they appear to be chasing the player, attempting to hit them etc. anything along those lines, not sure what could be done for non boss pets etc. but personalities could be added to them as well. The magic carpets are probably another example of followers/pets that have some sort of personality to them, they're a bit eh.. to me though.