I prefer out-the-top sheaths. Less need for a retention strap that will get in the way and probably be cut when re-sheathing in a hurry. I've got traditional Latin machetes and kukris that fit well in out-the-top sheaths without issue. The less I have to focus and think when un-sheathing or re-sheathing the better.
I understand that out-the-side may be the better, or only, option for certain styles. But if I
could use an out-the-top sheath for those styles then I
would. Therefore I have to vote for out-the-top.
Edit:
FortyTwoBlades
does this mean you'll be offering Imacasa machetes for sale through your site!?