While a few people have actually tried to play through a MMORPG without killing anything, for the majority of players a lot of the time taken up by these games is in combat. Thus whether you like a particular class' combat style is an important factor in choosing which class to play. Before I played the SWTOR beta weekend, I had planned to play a Jedi Consular as healer on release. But having played all 4 main classes now, I changed my mind.
The Jedi Consular, and his alter ego the Sith Inquisitor, are somewhat comparable to mages in other games. They have ranged spells that deal damage, and crowd control abilities to handle multiple mobs. So far, so good, but the devil is in the detail: The crowd control spells don't last very long (8 seconds for the first one you get, 4 seconds for the second one), and most of your "ranged" spells have a range of just 10 meters, which is awfully short. You can cc one mob in a group from 30 meters away, and then attack the others while they are running towards you. But that tactic fails if it turns out that the mobs are carrying blasters, and they shoot you from 30 meters, while you have to do the running to get into range of your other spells. Combat gets easier around level 9 when you get your companion, who is a tank. But personally I am not a big fan of pet classes (I never had a high level warlock or hunter in WoW because of that). Of course all classes in SWTOR have companions, but I'd rather have a healer or ranged dps pet than one in the front line. So while the Consular / Inquisitor are certainly very playable, I personally didn't like their combat style all that much.
I didn't try a Jedi Knight, but I did play the Sith Warrior, and I presume they work the same. The Sith Warrior was fun to play. Combat is very much melee, but there are enough other abilities to make that interesting to play. The damage output wasn't any worse than that of the Inquisitor, but defense was less complicated, being passive by better armor. That means less clicking to switch targets when fighting groups of mobs, and leads to a better flow. I might play a Jedi Knight and make him a tank, but I think I want my main to be a healer, and the Jedi Knight / Sith Warrior is the only main class that can't heal others.
I then played a Smuggler, which I assume works the same as an Imperial Agent. Combat of the Smuggler is ranged, using blasters and grenades. This is the class that has the only really NEW combat mechanic, using cover. When you target a mob and there is cover available somewhere, you will see a green ghost outline, and pressing the cover button or "F" will roll you there into that cover position. From cover you can use abilities that don't work when you are standing, like a charged shot. That works for small values of "works". The smuggler starting zone is obviously designed for the class, with rocks and crates placed just about everywhere to provide cover. But even there you often enough run into situation where there is either no cover, or the cover isn't BETWEEN you and the mob. You find yourself crouching behind a rock, while the mob shoots you from the side. Cover also isn't much use against melee mobs. Sometimes you just have to crouch in the middle of nowhere to be able to use the abilities you can't use standing, which feels a bit silly. But the grenades are a lot of fun.
The class I finally liked best for my future healer main is the Trooper (does the Bounty Hunter work the same?). The Trooper is a ranged class, with in my opinion better ranged attacks than the Consular / Inquisitor. He starts out with a shot that not only deals damage, but also does an AoE knockdown, which effectively doubles as a sort of crowd control. In spite of being a ranged class, the Trooper has good armor. And he still works very well in close range and against melee mobs. Unfortunately I didn't have time to play him up to the level where he gets the advanced class and the healing abilities. But I trust that he isn't too bad as a healer, and will try that class as my first character on release.
Overall I found the Knight/Warrior and Trooper/Bounty Hunter easier to play, in terms of clicks and keys to press per encounter. If you like more complicated combat styles with more buttons to press, the Consular/Inquisitor or Smuggler/Imperial Agent might be the better choice for you.