You can see all side-by-side here: https://www.ecb.europa.eu/euro/banknotes/future_banknotes/ht...
My takes:
Designs A and B and I are not terrible, but I'm not impressed.
Design C - the backside looks like the worst soulless corporate landing page graphics (Corporate Memphis style?).
Design D and E, H are okayish. Possibly I'd prefer something along these lines.
Design F has very strange coloring, the watercolor and sketch effect looks nice on screen, but I think more filled and more monochrome notes are more conventional and accepted, also some are bicolor. Not bad, but I'd not like it in everyday use probably.
Design G is somehow not good looking, I cannot phrase it. Both the font, and also the backsides scenes are meh, even the modernist buildings are better on some other series.
Design J : the creepy abstract cartoon people on the backside ruin it. Also somehow not aesthetically pleasing, but not catastrophic.