When given the option, 99% of the time I reach for a unseen, because honestly, most of those "older" designs look a lot cooler than the reseens (The new Warhammer for example, is fugly). But when that is not an option, the reseens are acceptable. They are the same mechs, just a different model, and that is fine. Although I will of course proxy, because there are many minis I do not own.