My apologies for dragging up a thread from the second page, but in choosing apple varieties for training it is very helpful to have only sorts that spur up freely and are not too vigorous.
Most pears are quite docile but apples vary enormously.
I have a trained Bramley but I would not recommend anyone else to try it, it drives me mad. I have not tried a Worcester nor would I care to.
Varieties that I have found amenable to training are James Grieve, George Cave, Laxtons Superb, Brownlees' Russet, Late Orange (with a struggle). I'm currently trying Fiesta, Spartan, Orleans Reinette and Ribston but it is too soon to give an opinion, need several years experience.
In the early years you may want to fill up the gaps with veggies. Be careful that they do not conflict with any apple tree spraying you might do. Alternatively you could fill up with extra apple trees and in five or six years dig out alternate trees: if you are careful they can be transplanted.
I presume you are buying maiden apple trees, pre-trained espaliers are budget busters.