We are looking at having one of the above done to extend space in our 3 bed end of terrace. We have a side return to the garden which we would want to keep so wouldn't extend to the side at all, only into the garden (single height).
Loft extension seems easier and would give us an extra bedroom which is more useful than increasing kitchen size (although both would be useful) but where on earth do you fit the stairs?! We have a very small landing so not sure how that would work, although loft is pretty spacious and high.