Do you want your collection to somehow match up in scale?
Well here are a few tips.
This is the way i do it and i think you'll agree
In order for Prime and Megatron to match up with the fallen, I Use the voyager class figures for these two.
As for Leader Jetfire, Well, He's a little out of Scale with leader prime, But he somehow works out well with the voyager prime.
Same thing with Ratchet, but with the voyager and deluxe figures.
The Contructicon figures minus Demolisher work out perfectly in scale.
Despite the fact that i have the deluxe figure, The legends figure for arcee works out as well, And i Think you'll agree.(Same with Legends Wheelie)
Devastator And Demolisher work out with both legends and minicon figures'
robot Replicas Prime works out well with voyager grindor/Blackout
Well thats all i have to say. If you don't agree and want to do what you want to do, then e my guest.