Its not just about exchange rates.. If you are wanting to convert Riyals to Sterling you are obviously thinking of sending money to the UK so you have to factor that in too.

As an example my Banks exchange rate today is 5.132 (!!!)and they then charge me a flat fee of 50 riyals to transfer the funds to my bank in the uk - which takes just a day - then my UK bank charges me 7 pounds to take delivery of my money - (robbing b@st@rds!!)

Compare that with the others and I think its a good deal.