For metagame purposes during the final semester, always Ryuuji and Ann, because full party charge+ concentrate are way too good to pass up. Last party member can be anyone, it just depends on what your looking for. Mona/ Makoto are good for debuffs/ heals, Haru has full party repel and her hybrid skillset works great with full party charge/ concentrate. Outside of Ryuuji and Ann, Akechi and Sumi have the strongest 3rd awakening skills, and very high strength/ magic stats so I usually have 1 of them in the party on the final day.

Purely for fun I usually use Akechi + Sumi + anyone else I feel like using, because they are only available for like 1 palace.

For Lavenza fight specifically I like Mona, Ann and Sumi.