I've built two GP kits:
PT-40 - great build, not the easiest trainer.
SlowPoke 40 - challenging build, okay flier. Thought it would be good as a first low wing but the short coupled nature of the plane did not lend itself to a good experience for me.

I've built five Sig kits:
Kougar - first RC plane - truly a builders kit - no laser cutting. Didn't last long as a trainer.
Sr. Kadet - challenging build, but the flying is great for a beginner! Much better than PT-40.
LT-40 - Great build - comes with most everything you need to put the kit together and laser cut. I soloed on this plane.
LT-25 - The easiest RC plane kit I have ever built - laser cut. Flies great, but has a tendency to lose the dural landing gear with not so perfect landings.
Midstar - Nice step toward a low wing trainer. Laser cut - easy build - good flier.

The point of all this - I like Sig better