I've always followed tradition, but if I was starting again (it is possible to convert boxes, but it's not easy, and you do need to have them all the same) I'd be tempted to use top. The problem I have is a tendency to lift the odd frame from the box below the one I'm lifting off the pile, as the bees link them with comb and they can be quite firmly stuck at times. I believe (I haven't put it to the test) that this is less of a problem with top bee space. As time passes, though, everything tends to get propolised, at least with my strain, and I then have the opposite problem, of trying to shift recalcitrant frames! It's not critical, and if you ever buy any secnd-hand boxes, they'll almost certainly be bottom space.
