This question would fit better in the "Agriculture Engineering" section, but there are some weird rules regarding revealing crossbreeding details. It's generally encouraged to experiment with crossbreeding instead of having people just give you the answers. The tiers and attributes listead at http://ftb.gamepedia.com/Crops_(GregTech) and http://ftb.gamepedia.com/Crop_Breeding_(IndustrialCraft_2) will give you a decent starting point, though.
However, you could also try the Crop Nei Plugin which would allow you to find out some good crossbreeding combos, without it being on the forum where the results could be considered spoilers for others who might still want to experiment.
