What’s the best recommended shuttle substance to supplement creatine with?

Without a doubt, a high-insulin carbohydrate, e.g. grape juice, dextrose, maltose. Maybe even put a glucose disposal agent with it such as alpha lipoic acid.

What works best for me:
1 scoop AST HSC last 10 minutes of workout. 2 scoops VP2 (or 1 serv GROW),1 scoop HSC, & 2 scoops Gatorade powder in 16oz water immeadiately following training.