I'd give the energy drinks a miss.
Truth be told, I do love the taste of Relentless. Their 'Berry Juiced' (or something along those lines) flavor energy beverage is honestly one of my favorite tastes, ever.
However, I have repeatedly found that no matter how much Relentless or Monster or Red Bull I drink, it never comes close to giving me the energy of one strong, freshly brewed coffee. I have always put this down to the idea that there is more going on within the chemical structures of coffee that contribute to increased alertness, than caffeine alone.
I do have a loved one who, at one point, was drinking 4+ Red Bulls a day, as well as taking several Beechams a day, purely for the caffeine. She ended up stopping after a few years, and now just drinks coffee.
In the UK, you pretty much wont find a public club that doesn't market some kind of energy+alcohol drink, often as one of their cheaper beverages. Makes sense for the proprietors, I suppose. Us Brits are notorious binge drinkers, but an unconscious customer cannot keep buying.
On the whole, energy drinks aren't great. They're generally full of sugar, and there surely can't be anyone left that doesn't know about the perils of high sugar intake. I also seem to recall an episode of the podcast 'Nutrition Diva: Tips and Tricks for Eating Well and Feeling Fabulous' that cited a study which had found that the combination of caffeine and sugar and carbonation seems to damage teeth faster than any beverage which is merely caffeinated OR sugary OR fizzy.
I have a friend whose energy drink use I actually have to keep an eye on. The boy buys those big litre bottles and just goes through them without thinking, and ends up a litre later and a shaky mess.
On the whole, I think they pose the most risk to kids and young teens, just because it's pretty obvious that a 'can of high' which kids are legally allowed to buy years and years before they can legally purchase the 'can of high' that is beer, is going to wind up being over-used or used incorrectly. If a 12 year old knows that they can buy this drink and it gives them a buzz and makes them feel productive and creative and clear-headed, and no-one bothers to explain to said kid that this high is really only meant to be used occasionally to combat tiredness or to help people get all of their work in before a deadline, the kid is going to pretty quickly try drinking more than one can, to see if it keeps getting better. They are also likely to share their experiences with their mates, and eventually you have groups of kids drinking Red Bull or similar much like teenagers drink beer. This includes both the positive and the negative, both friends gathering to share communal beverages, and the 'oh Go on, try it, it's awesome!' pseudo-pressure, and the who-can-drink-more competition. At that is simply not a good idea with energy drinks.
When I was about 13 or so, a mate came over who was a few years my senior, and his mother had given him a can of Red Bull. My own mother went absolutely bezerk, and refused to let him in until she had spoken to his mother about why he had been given such an inappropriate beverage (it turned out he'd been traveling back from a school trip all night and had not slept, so my mother begrudgingly let him drink it). I mention this ditty not just because I am incapable of writing concise, straightforward forum posts

but because I cannot believe how fast attitudes have changed. All the kids in my neighborhood drink energy drinks, and fairly casually. I've seen local shopkeepers sell them to properly little kids. Maybe it's the UK, maybe it's just the town I live in, but I damn sure wouldn't want to be one of the teachers tasked with controlling the almost totally caffeine-saturated youth around these parts. Can't help but feel there should be an age limit or something. If you're over 16, you can buy so called 'energy drinks', if you're younger than that, make do with coffee.
Also, for those of you chugging back sugar-free or low-sugar versions, do remember that artificial sweeteners can provoke a lot of the same blood sugar issues as real sugar. The body just knows too well how to react to sweet things, artificial or otherwise.