GTK+: can be a little overwealming but I was able to understand it alot better then xlib. It is slower tho i will admit.
never tried svgalib before but thanks for the link ill have to check that out.
GTK+: will confuse you on all its diffrent versions as well and for larger apps it can get a little confusing on what does what or how this is related to that.
ncurses: is cool but can be a freekin nightmare. i still dont understand colums
and rows
Qt: dont know anything about this think i made a program with it before i Knew anything about C
xlib: Try if you dare you might find it more understandable then me. Never could get my hello world program to display.