I've tried training, I think, in every single venue where it's possible thus far.
Kelp Beds: single trainer seems fun, but too stressful for me; I tend to prefer the two-trainer builds because I need to think on my feet less. Since you have a Culex dragon, one of these with a mage can pretty much get you through the Kelp Beds already, though it'll be slower.
Golem Workshop: oof, slow as anything. Not bad if you need to be in the Golem Workshop for some reason, but if you want to level fodder fast, I don't think there's any build that can make this competitive, especially since a mage is required. Nice to have if you want to train fodder while grinding for bosses or venue-exclusive apparel, though?
Mire: as you say, solid, reliable, can get pretty boring if it's used exclusively. Still, I used one of my free Eliminates to make a re-optimized Mire Flyer: correct element this time, so that I have options.
Ghostlight: I love my Anticitank. :D I haven't gotten an Eliminate from here yet, but I do feel like I get more drops, so staying in the venue for a bit feels less boring. Possibly because there are more 4-packs?
Harpy's Roost: Surprisingly fun for me! A little slow once you get into higher levels, but I was expecting it to feel slower than it ends up being. Still not optimal, but a nice non-Mire non-Ghostlight venue to hang out in for a while if you like.
Crystal Pools: Probably my least favorite viable venue: slow, no chance of Eliminate, and the bosses are one mage and one physical attacker, which means I'm constantly getting them mixed up and messing up my strategies. Sigh. On the other hand, it's very pretty if you like bright colors as much as I do!
Boreal Woods: Again, surprisingly fun, though honestly the worst place to level fodder competitively. It's ridiculously slow; I'd never recommend this to someone as their only training option. If you're going Yeti-hunting (…I've been here since 2013 and the Yeti has never ever dropped for me, and I need it to for the Coli Scavenger Hunt, so…) it's a nice way to get some other things done while farming, and it's a relaxing grind since the Yeti is more of a miniboss. All that said: Boreal Woods is the only venue I've heard where you can solo train safely without Eliminate, and you can probably take literally any of your trainers to Boreal Woods and do just fine. Definitely the Culex build will do just fine. So maybe don't build for it specifically unless you just like trying out new builds.
So basically… if you want another trainer, where do you want to be, what do you want to do, what elements are optimal? Do you want to farm lower-level venues at all? How important is speed to you? Etc etc. But if you have a Mire dragon and a Ghostlight dragon, I think you've at least got a way to avoid total venue burnout already. :D
…I know you've already gotten a lot of great responses, I just wanted a chance to babble about Coli for a bit!
