I have the same problem.
It's not anywhere near 100 shows...it's probably more like 20 or 30 though. What helps is watching them with friends because this way you can put series "on hold" until your friend is available and just watch other anime on your own accord. Like ones you're sure your friends are not interested in.
For example, I have a friend I can watch ecchi comedy anime with, a picky friend I watch high-quality anime with, and a friend who's more open to anime than the first two but doesn't like certain tropes so I know what shows to avoid with her as well.
This is going to sound extremely "geeky" but I can decide what shows to watch on my own by using the elimination process.
Friend A: Likes ecchi but hates horror/creepy anime. Likes romance but not love-hate romance.
Friend B: Likes horror but not vampires, likes cute stuff but not fan service, likes shoujo, but not stereotypes
Friend C: Likes romance but not violent tsundere. Loves dark drama and horror anime.
So I can deduce from all this that I will be watching
Zero No Tsukaima on my own.
I also make sure to set aside a slot of time just for watching anime. Normally I do it before bed but this isn't the BEST idea in the world for marathoning anime. It's too easy to pull an all-nighter.
It's difficult to choose the next anime to marathon...but I'll normally pick the one that weighs on my mind the most at the time and make that my priority.