For regular oil use Castrol GTX 10W30. I've been using that stuff for years and it really lasts. Even when revving the crap out of my car I get respectable milage on it between oil changes. BMW also recommends using Castrol GTX
Also, using synthetic oil on older engines will only make your oil burn away faster. Stick with the cheaper regular oil as it's thicker and won't burn as easily.
'02 C32 AMG @ 18psi - Eurocharged custom ECU/TCU, ASP 178mm crank pulley + NW PSK, CM30 i/c pump, NW i/c iso kit, EC i/c, Magnecore wires, NW CAI, SL55 Y pipe, NW ported intake manifolds + gaskets/spacers, NW inconel exhaust manifolds, NW catch can, dual exhaust, H&R sways, H&R coilovers, H&R spacers, Quaife ATB LSD, goodridge lines, Stoptech pads, AMG 18" rims, Zeitronix datalogger.