It depends on how you like playing/what your good at playing?
Do you like just having massive auto-attack damage?
Do you like being able to heal and protect others in your team?
Do you like to do huge amounts of magic damage?
Lux is a goOd mid lane Mage, but I wouldn't recommend her to newbies as she uses skill shots which are bait hard to aim. Miss fortune is good, and easy to play as well, because she is an adc, which means she auto attacks to deal damage. Cho hath isn't the best champion for ou to play right now, as he also requires skill to land his spells. Try the recommended champions which are 450ip. Keep in mind tht no champion is bad in LoL, just depends on how u play them.