Klizan's been around since 2007.
But he's still "just" 23 and has only just achieved any real familiarity. It's not really uncommon these days. As an example off the top of my head, Soderling turned pro in 2002-2003, but he wasn't on anyone's radar until he trolled Nadal on his way to a five set finish at Wimbledon 2007, 4-5 years later. Dogopolov, similarly, was/is considered a fresh face at 23. Other than special cases, like that so-called "super six" (Djokovic, Murray, et al.), cases like Klizan's have been the norm following the "New Balls" gen.
Anyway, for my part, I'd go with Goffin. As a somewhat jaded fan this year, I didn't follow the late season too closely, so Goffin is probably most notable to me for his RG performances.