Ardfallen are very good and super professional but they charge just as much as BMW so sorta defeats the purpose... Mark Murphy Motors are supposed to be very good but I don't have personal experience with them, and same with Murphy Motor Works.

If it's just an oil service I'd go to BMW they are always decent value, for the 335i it's 174 Euro
check bmwservice.ie and pop your reg in and it'll give you a quote.