Is a longer defrost better than microwave defrosting?
Microwaving meat to defrost it tends to start cooking it at the edges and generally make it go weird and rubbery (scientific terms I know). So yes, it is better to defrost 'naturally' in the fridge, in terms of quality.

Freezing damages meat by bursting the cell walls as their water expands. This affects the texture more than the flavour. The damage is done when freezing, not cooking from frozen, so the latter should not effect taste. The main issue with cooking from frozen is that if the item is big (say, a roasting joint), the outside can be overdone by the time the middle gets up to a safe temperature.