With time comes lots of different tries at sealing and that means there is likely no way to know what folks have used. If there are piles of caulk, you may have every type sold!
So what to do?
Choose the new as you feel right and there can be any number of good ones, partly due to marketing! For my tea, I like Dicor.
But one thing is true of all and that is they will work better if the area is truly clean. Many refuse to use some types if silicone has been used before as they feel new will not stick to silicone.
This is where I often tend to see it differently as I have some experience with resealing fish tanks, where silicone is the most common/prefered type. I have learned that it is not the silicone but the way the area is cleaned! Much like painting, the result requires good prep!
Clean the area of the old caulk, without regard for what type. Pileson topof piles shows bad technique. A small thin layer of 1/4 or less works better than a pile on top of one that is already loose!
Think like a raindrop! If you are running across a roof and come to a pile will it stop and find a way under better than comming to a smooth even edge where it is easy to go up, over and off?
After the pile is removed,scrub it down really good with alcohol/ paint thinner to get the film off before going with new.
I find great value in an oscillating tool for removing the old without gouges. I had a gifted high dollar one which wore out quite quickly but replaced it with this cheap one which has lasted very well:
https://www.walmart.com/ip/Hyper-Tou...2?athbdg=L1200