I have tried LoL, DotA, HotS, Smite.
Smite really isn't my cup of tea, I played a game or two and got bored. Maybe it evolved since I list tried it (almost 2 years ago, I believe).
HotS feels casual -- no need to last hit, focused on objectives, there are no (situational) builds (unless you take the traits into consideration). I tried it with some friends ( 5-man premade) and it was fun, for a couple of games, but I couldn't bear playing more. Still, I like the different objectives.
DotA (2) on the other hand feels like the opposite of HotS -- you will get matched up against veterans (speaking from experience here, maybe I was just unlucky?) and you run down mid and you can't last hit anything because the other dude is denying everything from you and you end up with 2 lvls behind and you just get **** on. Sure, git gud, but that's not that easy to achieve when you're tilted AF. Anyway, you invest some time into it and get to a point where you actually make a difference, you're strong and... and you wreck the enemy team. Again, speaking from experience here and I found it extremely hard or simply impossible to comeback or to lose once I had certain advantage. All in all, DotA 2 is clearly more complex than HotS and even LoL.
And now my pick -- League of Legends.
First of all, I probably play it over the other mobas because most of my friends play it also. What's the point of playing a multiplayer game if you're not playing with your friends? I'd get bored so very easily.
There are a lot of champions/heroes for you to try out, lots of builds and all that good stuff, but DotA has that too, right?
The characters are pretty dynamic, especially the new ones. There are objectives -- drakes, rift herald, baron (these 3 grant you buffs), towers, inhibitors and, finally, the nexus -- the big rock you have to destroy in order to win.
All I can say, guys, is that, if you haven't already, give LoL a try. You might like it.
I ended up in diamond last season and oh boy, I gotta say -- most of the community is ****, though (don't know how DotA's community is). Hang in there.
Have fun, whatever you are playing and have a nice Christmas!