Starting out in HotS can be a disorienting experience when coming from other MOBAs, however, you shouldn't worry too much. There are some heroes who are better suited for newer players and some that are not and the game is confusing on which heroes you should pick to start out with. However, don't worry, I've got your back with these surefire newb proof starting picks for the best heroes in HotS, especially when starting out.
The following list is aimed at heroes that are not only powerful, but powerful in the hands of everyone. As you play more and more HotS, you'll develop and find which hero is the most powerful in your own specific hands. For now though, these are the best heroes to start with.
Best Assassin - Raynor
Raynor is a point and click allstar. There isn't anything special to him, no gimmicks, and he's got a bonus get out of death free card with his stimpack. Don't think that his simplicity makes him completely ez-mode, with great power comes lack of depth, and he can get boring fast. Yet, when first starting out, only having three buttons (two actives and one ultimate) is impressive considering the amount of damage he can dish out.
A lot of newer players want to aim for Illidan, due to his insanely high damage output, but he requires some advanced learning when it comes to the game, such as when to engage and when not to, since his health is paper thin and he relies on the constant influx of health leech from each strike. Raynor on the other hand literally just has one major ability: his raw damage, has a good amount of health, and his beginner ultimate can rain the pain down literally (along with do some impressive damage to gates and towers).
If Raynor isn't your thing, I suggest looking at Nova. While similar to Raynor, she's got cloaking to make it easier to move around, but she's nowhere near as simple as Raynor. Valla is also another good choice, but her health makes her a bit harder to use when first starting off.
I'd avoid Illidan and Zeratul. Both require knowing the game a bit more. Jaina is great when you queue with a team, but solo, not so much.
Best Support - Brightwing
Avoid Malfurion, who is pushed onto you by the game in about five thousand different ways, and go straight for Brightwing. While not as easy to play, it's teleport and healing will make you an allstar in the game. If Brightwing isn't your thing, then Li Li is an easy second.
Avoid Tassadar and Malfurion. Malfurion is designed with specific teams in mind (at least from my point of view) and Tassadar, while powerful, is very hard to play.
Best Warrior - Diablo
Diablo has a ton of health, is penalized heavily for death (but comes back much quicker), and has an array of skills you can faceroll, making him a powerhouse for newer players and veterans alike. Diablo is strong in the sense that he's easy to play and very comfortable with charging into bases.
If Diablo isn't your groove, I'd look at Arthas who is very hearty and is a great team player with his snares and slows.
I'd avoid Chen, just because he's really good, but until you know the game he can be hard to play.
Best Specialist - Zagara
Zagara has the ability to summon tons of things at your enemies from a long distance, both newb friend and powerful. There isn't much to say beyond the fact that most of her abilities have her standing way out of the way of danger and launching an unending assault. Sgt. Hammer is similar, but with more direct firepower and designed more for the lategame.
Avoid Abathur and Murky. Murky's quick respawns and lack of giving the other team XP on death is GREAT, but he's also hard to do any damage with or achieve any objectives with. Abathur is a powerhouse, but he's hard to play and even some of the best teams sometimes don't see a value in bringing him along.
Until Gazlow is reworked, I'd avoid him just out of there being better picks. The rest of the specialists are pretty strong.