Fiesta is a modern (1970s) English variety from the East Malling Research Station in Kent. It is a cross between Cox's Orange Pippin and Idared.
Fiesta is a medium-sized apple, with the characteristic flecked red and orange flush over yellow - a very attractive autumnal colouring. It is distinctively Cox-flavoured and is juicy, crisp, rich, aromatic, and sweet. As well as a good dessert apple it is a very good variety for making your own apple juice from. In an average year Fiesta is merely a good sweet Cox-style apple, but in a year that suits it, Fiesta gets very close indeed to the heights of Cox's Orange Pippin. This can be a really good apple.
It stores better than Cox, a characteristic it inherits from Idared.
Fiesta is also an excellent variety for growing in the garden in most parts of the UK, as (unlike Cox) it is easy to grow and crops quite well.
The only minor disadvantage is that Fiesta grows in a bizarre straggly fashion, rather more sideways than vertically. Also, it is prone to toxicity and canker on acid soils (less than pH6).
In summary Fiesta is probably the best choice for the gardener wanting a Cox-style apple without the hassle. It is easier to grow in every respect than Cox's Orange Pippin yet comes very close indeed in the quality of flavour.