I've used Liquid Pro, and it's temps, when applied properly, cannot be beat. However, it's a royal pain in the ass to apply properly, and cannot be completely removed without lapping. And yes, it does corrode aluminum and is extremely conductive.
AS5 may not be conductive with the voltages you run into inside a PC, but it's capacitance can cause almost as many problems. More than once I've gotten a tiny amount where it's not supposed to be, and couldn't use a GPU, CPU, or mobo until I cleaned it off completely.
Ceramique is not the best performer, and takes even longer to set than AS5, but it's still within 2-3C of the best non-metalic TIMs after it's been worked in and it lasts forever. Some high performing TIMs (like Prolimatech PK-1 or TX-2) have worn out on me in 3-6 months when exposed to frequent and extreme thermal cycling. Even AS5 and Noctua NT-H1 rarely last more than a year in these situations. However, I have parts that have had the same application of Ceramique on them for 3-5 years and show no degradation in thermal performance. Furthermore, Ceramique is a great deal. It's less than a quarter the price of many TIMs.