Anything to have glucose levels normalized or up a tad. If you go into trainig with even slightly depressed blood glucose, you can and will more than likely have a bad time. Interestingly enough, it really only takes approximately 5 gr. of carbs to raise blood glucose back to normal levels.
Depending on how far out your training session is, as to the type of carbs you want. If relatively close to training, then a bit higher glycemic is a good idea. Longer away, more fibrous and slower digesting carbs.