All usable GUI toolkits suck. However if you want broad portability and a sane toolkit your best bet would be the Enlightenment Foundation Libraries (EFL).
The EFL are written in C and focus in both performance and portability all the major platforms are supported (and then some). Wayland is also not an issue the latest release(1.10.1 as of this writing) and the next one to come should work without issue in even a "pure" Wayland environment. -- Regards, Alex-P. Natsios (a.k.a Drakevr)
