Unity is good (at least for me) only IF it's implemented a gallery and you can view again all the lewd scenes.. In a Penpy game, by default, you can access all the previous saves and lead on (it's tedious to do but at least it can be done).. I think this is one big difference between others on both engines, just like what happens between Renpy and RPGM.. Mystwood Manor used Unity engine but the DEV there put a gallery for each character with all that was good to review... Other than that, I don't see any difference in terms of graphic performance or other issues..