Good question. A controversial topic. When I rebuilt my brake system on my P210 (1967), converted to front discs, about 10 years ago, I went with silicone based on what I read at the time. (Somehow I got the impression that the more a car sits for lengths of time, the better the silicone option is). Although I drove it to work today, it is not a *daily driver* so I thought silicone would be best. I had no trouble ever with the brakes throughout the last ~10 years until...

Several months ago, given that 10 years (15?) had passed since the brake overhaul, I thought it best to flush the fluid and replace, intending to replace again with silicone.
A lot of gunk came out and in the process the master cylinder went bad.

I replaced the master cylinder with a new one (at least the second new one I installed in the car) and, again based on current reading and knowledgable mechanic advice, this time I replaced with Ate racing fluid (non-silicone). I probably flushed the system 3 times over. As of this morning, all is good...

Point is - you'll find differing opinions on this, all from knowledgable people. Current consensus appears to favor non-silicone.

Best of luck

KaiS