Both matter, but the bridge significantly more-so to me. For 5 strings I have a max of 18mm before I start fumbling over myself, and 17.5mm is the sweet spot. On 4's it doesn't matter quite as much, but the standard 19mm works well. As already mentioned by others, the neck profile is far and above the most important thing to me and the nut width and string spacing all play a part in that as well.
