The obvious solution is to only ever release them in two-packs with ambiguous labeling.
This is what I've been saying they should be doing with Rumble and Frenzy for years!
But anyway, my arbitrary thoughts on alternate Megatron alt modes...
Tank- probably the most logical and arguably the "closest" to his origins since it's basically a big gun on treads, and was his immediate post-gun alt mode so it's got lineage behind it. Doesn't fly though, which hurts the "rise up!" rallying cry.
Helicopter gunship- my personal preference. It's still a play on his G1 form, because it's got a giant gun, and the flight based mode allows for the double meaning of "rise up!" as a counterpart to Optimus' "roll out!" It's also not a jet, so you get the positives of a flight based alt mode without stepping on the Seekers' turf. The blades also give you an opportunity to work in the G1 Megatron sword in a more seamless way.
Stealth bomber- like the helicopter, it's a flight based alt mode that doesn't infringe on the Seekers, so it's got a lot of pluses. Problem is... I kind of like a stealth bomber as a vehicle form for Soundwave.
Jet- I'm a shameless MW fan so this does have some appeal. The problem is that MW Megatron in his teal colour scheme is just such a unique look that I'm not sure it's got legs as a Megatron design going forward unless it's a specific remake or adaptation of Machine Wars. Still, I adore it and think it's done nothing wrong.
Outside of that, a fighter jet Megatron in broadly G1 colours doesn't really work for me because it seems like it could infringe too much on the Seekers. Starscream especially, given Megatron and Starscream's similar colour schemes.
Truck- look, I loved Phantom of the Opera sadsack
Megatron from DotM, but I don't want to see "truck Megatron" become a regular thing. We already have Motormaster, Scourge, Nemesis Prime, and Toxitron. Not to mention Nova Prime who's sometimes Nemesis Prime. We don't need Megatron to be a truck to get "a dark reflection of Optimus."
Satellite- that ABC pitch is fascinating because while I don't think it would work in totality, it had some ideas about Megatron that I like and would like to see played with. Even back in the 80s, there was some discomfort with the idea of Megs as a gun and the satellite was pitched as an alternative. There is a cool look you could go with if he turned into an orbital weapons platform, but the problem is satellites don't move under their own power. I know the space shuttle was never as maneuverable as Astrotrain and Blastoff were depicted as being, but a satellite just relies on gravity to slowly move through space. It's a cool idea but I think it's something that would limit how often Megs could actually transform and do something useful.
Alien whatever- there is a degree of logic there, that Megatron is so arrogant that he may not think he needs an Earth disguise or view an Earth alt mode as beneath him. Still... this never totally worked for me? G1 Megatron turned himself into a pistol, the idea that he'd see himself as "above" an Earth mode isn't rooted in anything from the canon. It also bumps up against one of the appeals of Transformers, that you can turn these characters you like into vehicles or devices could recognize. Sure, Cybertronian modes can be fun, and may even work as the primary look for some characters, but it feels lazy to default to that for the franchise's major villain.
So yeah, helicopter gunship would be my preference. I'd love to see Animated Megs get a Generations update, but I'd also love to see the alt mode adapted across more versions of the character. Give me an updated G1 Megatron with that alt mode. I'll happily buy it, even with the new stupid tariff pricing.
