Back when I leveled (1.5 years ago) on CN, I used the bopae from the Demon Roulettes. I recommend skipping Red Lotus and Senior 4 bopae because you will outlevel the content very quickly. Instead, focus on 24man bopae like Pohwaran. Also, you can go for Mushin's Tower bopae (Floor 7)
Reasonable bopae sets pre-50 would be those gotten from hero token exchange or from the newbie free gift event. Don't worry too much about getting good bopaes before 50. If you are in CN, your level will shoot to 50 in no time.