Which is best Metformin or Glipizide? Is there a complication if I take 2 glipizide 1 Metformin in a day, 8hrs in between.?

There is no "best." It's what works best for you and has the fewest (or better yet - none) side effects.

The only issue with taking both Metformin & Glipizide is the potential for hypoglycemia. But if the doctor prescribed them and that is what it is taking to get you glucose under control, then you should be fine.