I am a level 13 player. And ever since I started league I've been an ADC main. My champions that I've used are
and 
. As I started playing more and more matches, I started to notice that the matches I lost that we had at least 3 ADCs. So I planned on changing my role. I thought that the role of a fighter(such as 
) or a support(such as 
or
) might suit me well. I wanted to know what you guys thought, Which will be a better transition for me?
Find some champions you enjoy playing.
I personally lean towards tanks and fighters.
Some people lean towards mages, ADCs, and/or assassins.
It's up to your personal playstyle and preferences.
Try for various champs, and then play the ones you like the most
then the role you should play will automatically be clear to you once you will deepen the knowledge of your preferred champs
you could kinda do both. there are some ad fighters that itemize like casters, as they get most of their damage off their spells, going for cdr and armor pen instead of attack speed.
Considering who you use, I would say APC.
Although APC and support are two very different things. Just saying :)
