Best type of bike lock (materials, style, etc.)
Get the kryptonite fahgettaboutit - as small as possible.  Kryptonite 997986 18mm New York Fahgettaboudit U-Lock,Black Mini 

Best lock out there. Because the shackle is 18mm thick, I don't think you could cut it with bolt cutters, so you would need a hydraulic jack -- but the opening is too small for a jack to get through -- that's the main reason to go for a smaller lock, so there is no room for the jack; or, a disc grinder to get thru it.