I'm not totally sure what you mean by 'branching out', but here's my suggestions.

From G1, probably Galvatron. Scorponok could work too, but he's a just a little bit big for what you say you're looking for. That said, it might still look good given you have more Autobots than Decepticons.

If you're alright with non-G1 toys, the recent Leader-class Megatron might suit your needs.
Masterpiece Black Convoy is another good possibility. Probably kind of expensive though.
It's a little bit different stylistically than the old 80s toys, but Transformers Animated Megatron or Shadow Blade Megatron could be a good fit too.