If somehow, there is science beyond Einstein's which allows interstellar travel in less much than thousands of years. If we are or have been visited, I think that it is more likely that the visitors would be humanoid (shaped like humans) at least in the basics.

They would have had to evolve as tool user, so two eyes for stereoscopic vision, something like arms and hands for tool using, something like legs for getting around and lifting heavy things, a mouth and ears for language, a nose to tell if their food has gone bad Etc. some of those things might be more or less evolved than their analogs in homo sapiens.

The famous gray aliens are a pretty good projection of what a human evolved for space might look like, Gracefull, hands, light bodies, certainly they appear to have proportionally very large brian pans. But they appear to be either all male, or not mammals. They have very small hips. If they were mammals like us, can you imagine how much trouble their mothers must have giving birth.