I have used Merck Chromolith C18 columns extensively and I highly recommend them. I purchase them through VWR Scientific. Although they seem pricey, they have allowed me to carry out separations that would otherwise be impossible with pelicular columns, all with blinding speed.
This includes using isopropyl alcohol for reverse phase separation without having to use excessive column heat. Separations that used to take 85 minutes with re-equilibration now take 22.
I could go on and on.
Buy one and try it, you will not go back to pelicular columns.