Robinson's is much deeper having top men from several era's Armstrong's included. I'm not sure beating Ross at WW trumps beating Galivan at WW. Although Armstrong had around a 10lb size disadvantage, so it is comparable to Robinson-Lamotta except RObinson was probably giving up similar weight to the amount Armstrong gave up against Garcia (just checked he gave up more weight in his first Lamotta wins)
Armstrong has a ridiculously extensive resume but there is an argument for Robinson having fought in a better era. Had Armstrong come around a few year earlier he would have had to compete with the likes of Tony Canzoneri, Jimmy McLarnin and Kid Chocolate, among others. Lou Ambers and Barney Ross were still going strong though.
There's not much in it either way, although if I had to choose I'd go with Armstrong narrowly due to the constant size disadvantage he had during his fights.
