First, I want to say that I've never re-wicked a bottom coil clearo. That said, I can't stand silica wicks

I think they had a nasty flavor, no matter what I did with them. That's a total personal preference thing, and why I gave up on clearos very early on. They just never performed well for me, or gave me anything close to a really good flavor (I had one CE something that was ok for a few days, but that was it). I recoiled and rewicked a Vivi before I got an RDA, and I used cotton, and it totally changed my
vaping experience. It still wasn't great (I hated the Vivi Nova), but it was a lot better than the silica had been.
My friend never noticed a bad flavor and loved her clearos, so it's probably just something weird with my tastebuds. So, I always go with cotton, and I love it, but I would suggest trying both before deciding for sure what you want to use. Some people think cotton is a pain in the ...., some people love it, some people don't care if they use silica or cotton and are perfectly happy with either.