I had a day off today, so I decided to mess around with character generation a little bit to better familiarize myself with the system. My Fighter (a Wood Elf named Tharis) went pretty much how I expected. For my second character I decided to finally work up a concept that I've had in my head for a while. Derndolfin Dwarrowhelm is a Dwarven Bard with a mildly quixotic personality. He arguably has too high an opinion of himself, but he's jovial, generous, and always has a good story to tell so most people don't mind. Plus his name just begs to be used in a work of alliterative meter. He looks fun mechanically, but Bard's are kind of all over the place and I'm not sure how effective he'll be.
In general character optimization (I'm assuming combat optimization here) is not intuitive, and it doesn't seem like there are any "easy answers." True, like with any game some choices are better than others, but the way abilities work encourages you to spread your points out instead of focusing them on one or two really high abilities. AC, PD, and MD are all based on the middle of 3 different scores (Con, Dex, and Wis for AC, Str, Con, and Dex for PD, and Int, Wis, and Cha for MD). While this theoretically makes each score less important and encourages more build variety, those with an eye toward optimization might feel restricted. Unless your class uses Int or Cha for something, any other score is probably a better choice to invest in. You could also make the argument that the system doesn't really cater to optimizers in the first place, which is actually fine by me but I can see some people not liking that.
The last thing I'll discuss is the Ranger, with the caveat that I'm looking at the class in a vacuum and there may be other variables that would reveal themselves in play. This point runs counter to my last point in some ways, because the Ranger (while simple) looks like it will emulate 4E's incarnation in that it's a huge damage monster. A Ranger with an Animal Companion and either Double Melee Attack or Double Ranged Attack will be pumping out 2 or 3 attacks each round. The animal companion gets its own attack (either before you or after you, depending on what kind you have), and then on natural even results you get to make a second attack via your Double Attack option. Given how 13th Age damage scales (each attack deals a number of damage dice equal to your level), this will add up quick. Especially since the difference between a two-hander and a bow or 1-handed sword is 1d10 vs 1d8, and both of the Ranger's attacks get to add Str/Dex to damage. Thankfully the Animal Companion's damage is lower, but it's still nothing to sneeze at.
The Animal Companion also shares healing when you spend a recovery and it's next to you, so combined with it's separate HP pool it's actually a very efficient damage sink as well. The Ranger's base AC in light armor is also only 1 less than the Fighter's in heavy (14 vs 15), so defensively he's in pretty good shape too. Things get even sillier when you bring the poor Barbarian into the mix, since he only has a base AC of 12 in light armor (though admittedly he does get to use shields without penalty), doesn't get the damage sink capacity of the animal companion, and for some reason has the same base HP factor as the Ranger (instead of a higher one like the Fighter and Paladin). At least his recovery die is bigger, but he's still behind the Ranger defensively. He also gets a talent that lets him use a recovery as a free action when he hits 1/battle, but the Ranger's HP efficiency is still better than this (not guaranteed, because you have to hit) self-heal and it comes with the animal companion's extra attack. And if you were wondering, no the Barbarian does not make up for it with better damage (as far as I can tell). They can cleave once per battle (if they're adjacent to a second enemy when they drop the first), compared to the Ranger making a second attack on EVERY even roll. They also have a few talents that add some damage dice to their attacks situationally, and one that lets them split damage between two foes (but each takes half of the original damage).
Perhaps Rage (which lets the Barbarian roll 2d20s for his attacks in the battle he uses it, and increases his crit range to boot) gives him enough spike damage to make him worthwhile, but as far as I can tell the class is noticeably weaker than the Ranger. I'm not sure which class is closer to the baseline of the others in the game (i.e. is the Ranger really strong, or is the Barbarian just weak). Part of the reason I focused on just these two is that they're the simplest classes in the game, after all. Perhaps most other classes lie between the two on the class balance spectrum, but it's still a noticeable problem since these two types of characters often have very similar combat niches.