I tried them both and I agree, the traditional was a little more comfortable but for convenience sake I'm using the slip-on version right now. I did conserve enough length to be able to use either, tho.
The main thing with huaraches is getting the laces tightened just right for you. That's more of an art and needs to be experimented with. For example, the only lace that works for me right now is the traditional Tarahumara-style wrap that goes up over the lower leg. Looks odd nowadays but works awesome. :)