Here is a shot of the Snowspeeder that came in the MPC AT-AT on the right
compared to the larger Bandai mech collection Snowspeeder in the middle
compared to the Fine Molds/F-Toys Snowspeeder on the left which is even slightly larger than the Bandai
The Bandai and F-Toys ones are thought of as 1/144, but I actually think they are both closer to 1/110 or even 1/100. I feel like the MPC one is actually closer to 1/144 than either of them
As far as pairing, my personal opinion is the F-Toys snowspeeder visually feels like a better match for the MPC 1/100ish AT-AT closely followed by the Bandai one as both seem on the larger side for the Bandai 1/144 AT-AT. However details are light years ahead on either of those compared to the MPC one.
However, I think they can look good with either pairing
The way those scenes were filmed leaves us with very inconsistent scaling based on what filming models where used in the shots. Sometimes the speeders look really big like in the foot crushing scene, other times they look really small. Also does not help that the figures they put inside the large filming model are basically just torsos making it hard for a real person to fit in something full size at those same proportions
So in the end, go with what you think pairs best
for other reference, here is the Bandai 1/144 with some 1/144 scale figures and the Bandi and F-Toys speeders
As far as other things that are close in scale
The MPC Imperial shuttle or the Jazwares (aka Micro Galaxy) IMperial shuttle would look great together with the MPC AT-AT in an Endor Landing platform diorama
Or the Revell U-Wing is fairly close in scale (maybe around 1/90), as is the smaller Revell snap kit (it is around 1/110)