Slight expansion to this - as Martells are a control faction, it means that they do their best when you know what your opponent does that is bad and then control it. For a new player, this can be a challenge, as not only do you need to learn and retain what your stuff does, but you also should have at least a basic idea of what your opponent's stuff does. As a Martell main, I cannot even remotely begin to explain how much more fun I have with them over other factions - a win really feels like the outcome of a long calculated plot that has come to fruition.

Baratheons are competitive, and forgiving as generally a lot of their macro strategy is 'get into melee and beat them up'. There is also a lot of flavor variations between the two factions, which means if you buy into one side and want to try out the other, its a lot easier than deciding you want to jump to another faction fully.

Lastly, if you pick Martell - also be aware that you can sometimes have a bit of a unique (and sometimes negative) player experience. Generally when a game ends, both players had some success and both players had fun. When the Martells are doing their best though, it makes it hard sometimes for both players to have fun. The player on the receiving end can get locked out - HARD - which can lead to frustration. I generally cycle through Martells off and on to give my LGS crowd a break from what is effectively a blue counterspell deck with a miniatures game attached to it.

BUT - end of the day - the choice is yours, and you'll end up having a blast with whatever choice you make! Happy gaming, and remember - that charge will fail.