What to do when stuck between pursuing 2 startup ideas

Hey everyone! Need some feedback on 2 ideas I have and some general advice on what to do when stuck between 2 ideas #Idea 1: Tag based, shareable bookmarking web/mobile app, also has a reminder feature so that you won't lose forgotten bookmarks again. Thinking of starting with a niche like foodies and maybe expanding, but main problem I want to solve is a more organized central app to save, sort and share everything easily. Issue with this is it seems to be quite a crowded space, a lot of players and other people I see also building something similar #Idea 2: Everytime before I decide which unit to take, I always scour the internet and reddit to find honest reviews by students, because I find reviews by students on how the unit is ran and the content is the best way to validate a unit, helps me get a head start or decide if I want to take the unit or not. Official university unit surveys are private as well so I can't use that. Therefore, I am thinking of building a central platform that allows students to give reviews for other students to see, be it warning about some issues about the unit, or highlighting the strengths etc I would love to hear feedback on these ideas and which one to pursue or how to decide which one to pursue as I'm so conflicted, thank you so much for your time I really appreciate it!