ssh -X works fine depending on the toolkit you use (i.e. not Gtk, because of its rendering pipeline) and the distance/latency you travel. For distance/latency, at some point (i.e. at sufficient latency) you're going to need to think about you present this to users (this is true independent of the medium, there are hard physical limits that cannot be waved away), and so for any tool that promises remote graphical access will need to design with distance/latency in mind (e.g. vim works great over latencies as you basically queue up instructions).