Robert would talk about Viserys military more then his other stuff. Bloodied sailors with lots of ships and a trained military force that is bloodied and won a great victory.
Jon about Viserys political abilities. Got to take the cities without any real trouble from the nobles and citizens.
Tywin will talk about Viserys intrigue and show of power. Like killing rebel noblemen in a certain way and just destroying noble families. Show that Viserys can and will get you if you cross him.
Would love to hear their real take on Viserys. Not what they tell the public .
The problem here is I can see Robert viewing the Legion as a worthy foe, but he's too blinded by hatred to pay Viserys much mind as anything other than a beast to put down.
Jon is too contemptuous of things like actually
administering, much less economics and trade, so I can't see him being able to see past the surface level of Viserys being a sorcerer.
Tywin is actually... probably fairly moderate in his views when trying to actually get someone to see how Viserys shouldn't be underestimated, though his view is likely still dim.
The kind of perspectives y'all
really want if you want an objective view not mired by loyalist or royalist tendencies, is from people like...
1) Randyll Tarly
2) Wyman Manderly
3) Varys (if only because he's so outside either circle)
4) Olenna Tyrell
5) Stannis Baratheon (he forces himself to be objective)
6) Roose Bolton
7) Paxter Redwyne
All of these would make good "Viserys Targaryen" interlude fodder. We basically got a peak at Randyll, straight forward "how do I guide my House through inevitable war". That's all he's largely concerned with. The man's a battleaxe.
Wyman seems to respect our chops, but he's shown he's largely concerned with protecting his liege.
Varys is
largely the most well informed "Westeros" character, and he was likely the one to realize we had gone from "pawn" to "existential threat" first before all.
Olenna is shrewd and likes to lay things out as close to how she thinks they really are as possible, so any bias is more to do with apparent wisdom than anything else. Having one woman of great influence giving her thoughts also stands out more.
Stannis is bound to be loyal not out of love but duty, and has had personal one on one interaction with Viserys and seen much of how he operates on a political level, so he's bound to have some insight on some of his moves overseas and in Westeros.
Roose for that sticky vile take and a bit of insight from his perspective on our courting of the North. He's a schemer and there's really few Lords who both wield military power and plot regularly out there.
Paxter because he's met us before, and he's gotten a first look of how we
really are. I don't mean how we paint ourselves when parleying with Westerosi lords, or how we go around with the common people who's own perspectives blind them to certain realities. Viserys, who fills an entire room with his presence like another man lives and breathes, and the visceral reminder that an almost-polite conversation between him and a dangerous fey noble could have ended in fire and death, with all the honorable knights and a high lord of the Reach being ignored as they dueled with words as much as minds, were it not for the fact that Viserys was surrounded by swords twenty or thirty feet away at most at all times and utterly in control.
Really, Paxter has had the most opportunity to see us in a not explicitly "he's my enemy/he's my ally" type situation for an extended period of time. He'd make a good interlude.