Just my thoughts, I'm by no means an expert.
There's a reason you're seeing so many undead - because of all those runt teams.
Anub Idol, imps, and other humanoids are also common, and undead are great for countering them. I'm a very big fan of undead myself and use them on pretty much every team I make, so my suggestions will have that bias.
You've got a level 25 Valk, she is very strong. I don't have one myself but I sure hate seeing them.
You might want to take her for a spin. As for what to team up with her, something that can fight critters (since they are strong against her) and something that can fight aquatics (since she is weak against them). I actually don't see a lot of critters being brought into battles myself, but a lot of other pets have critter attacks.
You've also got a fair number of DoT users at max level or nearing it - oozling, glowfly, spiders, snakes, razortooth, etc. It might be worth a try to combine them with something that has Call Lightning. I find that DoT teams can be fun, especially when combined with a pet that can force-swap the dotted up enemy into the back row to slowly die. But the downside is if you come up against a team with a lot of Stoneskin/Shell Shield/Emerald Presence available, you'll get stomped because you won't be able to hurt them.
Your Warbot is a pretty strong mechanical pet and a lot of people enjoy playing mechs. I might set him up with your Fel Flame or Water Waveling and then one of your moths or maybe a humanoid, and see how that works.
For fighting those undead, I'd suggest looking at a rabbit, a good frog, and also some pets that aren't critters but who have critter attacks. I wouldn't stack a team with more than one critter since there are a lot of beast attacks out there. Because I love my undead so much, I use a Blighted Squirrel fairly often to beat up opposing undead.
Looking over some of the rest of your collection, some pets I'd suggest leveling would be the Crow, Fiendish Imp, Darkmoon Zep, and Chrominius. That's just for starters as you've got a lot of great rare pets at low level.
I never see anyone else using it, but personally I adore my Plump Turkey in PVP. I'd also suggest, when you can, replacing your Nexus Whelpling, Blighthawk, and Flayer Youngling with rares (or stoning them) and then leveling them up.
I'd also put a plug in for just picking a favorite pet of yours that you seldom or never run into on other teams. Then look at that pet's weak points and fill the rest of the team around those. I say this because everyone expects to encounter runts, direhorns, clockwork gnomes, etc. They build teams that will counter these common pets and more importantly, they know how they work. By now most of your opponents already know they just need to swap when they get the speed debuff from your runt, before you can stun them. Put in a pet they're less familiar with and they won't necessarily have a strat ready to fight it.
Um, not that I do that last one. I have two skulls, a pet a lot of people use, and feature at least one of them on pretty much every one of my teams.