Best Middle ?

Pick a handful of mids, you can do it either at random or just based on who you like the most. Try and get like 3.

Try not to focus on playing just one of them, you want to have the ability to switch into something more comfortable base on team comps. It's fine if you find yourself best at one of them, but in those cases I'd urge you to still try to go outside your comfort zone and learn the other couple you chose.