SRAM or KMC or other up to a 9speed version.
Buy on price and which looks prett to use.
Been using KMC X8 and X9 for a long time, but recently DRAM PC-850/9 something or other numbers and also really liking the lower down cheaper KMC chains too.
I have a few other brands I've fitted to a commuter and it's been grand so far, can't remember the name though.
Edit: it might be YBN, would certainly use again.