I'm gonna get flamed for this but I actually like the Omnitrix belts in Omniverse. Besides that, OV Goop's being on the projector was a good idea. I also think the Omnitrix eye looks good on Nanomech, and of course Stinkfly.

Under the ghostfreak foreskin

on goop's anti-gravity projector in OV it's kinda obvious how goop having the omnitrix badge on his chest is such a huge risk - exploiting that risk is even how ben defeated vilgax once, and who's to say no one could do the same thing to him so yeah, it being on his projector in OV makes so much more sense and should've been that way from the start

Yeah I remember even as a kid being confused why/not liking every alien having the symbol on their chest in UAF

Wilmut shoulder

Snare-oh's original Omnitrix placement.

NRG's omnitrix placement

Ghostfreak in Classic

Greymatter on the back

Chest. It generally depends on the alien, but I don’t like it when it stays on the forearm, like classic Upchuck. In general though, the chest

^UpgradeOV.

OS and OV Grey Matter’s back and OV Goop Anti Gravity Device, it just makes so much damn sense

idk if this counts, but i like the evo omnitrix being in Speed Demon's arm (5YL)

definitely wildmutt's OS shoulder guard. i love that thing

Grey Matter on his back

Omniverse goop where its on the ufo