What should I buy

So now I have3150 IP and I'm not sure what to spend it on. I own...

• all the 450, and 1350 champions, and xayah and lucian (from loot boxes).
• I have AD marks and quints, AS quints, AP quints, MP marks, armor seals and magic resist glyphs. What should I buy? more HP for those odd AP mid games, or more fun champs? If so what champions you suggest? Make sure the champion is fun. I'm down to listening to any suggestions.