I looked into airport transfers because our return flight was so early in the morning and we couldn't get a bus.
I came across Canary Forum on Trip Advisor and am so happy I did! Easy to book, paid in advance so no worries about having cash when you arrive or having enough cash at the end of the holiday.
Our flight was early but we were still met by our driver holding my name up at arrivals. The car was just outside - a new and comfortable car - and the whole service was professional at all times. The driver comfirmed our return trip and we were picked up at 4 am the following week as arranged. 
I'll never wait for a bus or taxi in Gran Canaria again! 
Highly recommended - just go ahead and book, it makes arriving and departing so easy!