[wim]

In my view, the differences are slight, except one: the so-called 'relaxed' bikes have longer headtubes, which make it easier to raise the handlebars to about the same height or slightly lower than the saddle. Whether or not that's important depends what you intend to do with the bike. In general, fast, competitive rides at the limit of your abilities are easier with a lower handlebar; a higher handlebar might be better for more relaxed riding just to get the miles in.