Depends on how much you want to spend and how likely you will get good quality results. For the most (£30+ per film), but the best chance of good quality then either Process C22 or Film Rescue International would be best (Do not bother with Old Film Processing, I don't know how they sleep at night charging what they do).
However for the age of the film, if you send it off to a good pro lab like Peak Imaging or Club 35 then your highly likely to get a good result for a reasonable price (£10 per film with scans). What sort of film is it as that'll give an idea as to the age of it?