Landscape, portraits, not professional

Which camera is best for you depends on why you're looking to replace the G10.

The G1X has far superior low-light capability and image quality (thanks to an image sensor that is 6x bigger).  So if image quality was your concern then G1X is a great step up (but note that the zoom is only 4x on the G1X vs. 5x on the G10)

However, if you want a more powerful camera that also gives you the flexibility to switch lenses then the T2i is an excellent and affordable entry-level DSLR.

I would take the Nikon D5100, because of it's good low light performance and amazing image quality.