Thaumcraft 4, just too much polish to ignore, plus it has a tonne of addons to enrich the experience.
Also out of the tech mods while I don't utilize it that much, RotaryCraft has to be one of my favorite tech mods. Not so much becasue it's fun but becasue it really tries to respect your intelligence, very little of it's dumbed down, has minimal hand holding and really needs a player to use that old grey gunk residing in your head. It's also got a great effort vs reward ratio, even to the point where it might be a tad OP.
That being said I do find tech mods to be a bit boring, not bad but means to an end sort of stuff not worth getting excited about.