So I found that a number of my minis look okay with the Transformers. I thought a lot were bigger than 25mm, but I realised that they're mostly all 25mm scale, but different games have different styles in sculpting the figures. Some figures, like Games Workshop ones, look huge and out of scale, because they are 'chubby' over-muscled and thick-limbed figures with heads almost twice as big when compared to others. My Doctor Who minis are much thinner/frailer sculpted, and look okay, and the Descent fantasy minis in the previous post look a good scale, because they are thin/frail thickness sculpted. When sitting them all next to each other, they're all the same height scale-wise, but the proportions (things like head size) make them look like they are different scales. So GW figures are out, as they look huge and out of scale, even though figures like Imperial Guards are the correct height.
Anyhow, my bonus for the day was that I found my civilians (a collection of 1930's American civvies) are the perfect height, and they have physical sculpt proportions, that make them look the same scale as my Legend Class / Scout Class Transformers and Gobots. So I've got about a dozen different civvies to inhabit my city of the future.
Here's two civvies painted up, and in the background is a UNIT soldier from Doctor who.
For Transformers scales, regular things like cars, vans, utes, etc, seem to work great in the Scout Class / Legends Class, I think. That's about 25mm scale with figures. Big vehicles, like large trucks or aircraft, will probably work best with bigger classes, like Deluxe Class. Here's a Deluxe Class Optimus Prime, and the scale between the cars and the humans with Deluxe sized Optimus seems about right. That's good, because I quite like some of the Deluxe Class sized models of things like Optimus (big Truck Cab), Megatron (tank / artillery mode), Starscream (Jet Fighter), etc.
I think Deluxe sized Optimus here looks about the right size, when you compare with comic books and the 80's cartoon, and I could picture the 25mm humans sitting and looking out his windows.