Depends on the person. But most all of them have one thing in common, caffine. If you are adverse to caffine, it may not be the best. I have found the best time to take them is just prior to your workout. Caffine at this time with a good workout will not allow the more 'negative' effects of caffine happen to you. Kind of like sugar pre workout as compared to other times.
-------------- Baseball is the only field of endeavor where a man can succeed three times out of ten and be considered a good performer
Definitely, pretty much any energy drink maker out there has a sugar-free version. I prefer either the Monster or Rockstar but there are TONS of horrible ones out there as well so choose wisely =).