I use the simple mobile site, which has no quote (its way faster and lighter, then the other).
All the ways mentioned above aren't good.
Finding a yiddele that has his little underground exchange place, as they have by far the best rate.
As a general advice to know whether a place has a good exchange rate or not.
Ask them whether they have fees, and you the ask the for the buying and selling price (eg $ to £ and £ to $), not tellong them what you intend on doing.
If the numbers are very close to each other, you have a good rate.