Some great comments and suggestions here. I am often involved with such things since I Coach Executives and their direct reports. Anonymity is King at the outset. How employees experience almost every aspect of how you set the stage and then conduct this will determine how well it works. Simple is better. Three samples might be...

What is most getting in your way this week?

Who deserves an Award for what they did this week?

What have you been measuring this week?

And by all means somehow publish all the responses you get from whatever method you use

The worst split at the top is 50/50 because it is asking for gridlock. Someone has to have the final say and that is the CEO. One of the jobs of CEO is to evangelize about the vision. If that is not quite happening, check the evangeilzing methods, check the present vision (it may be a tad off).

I have been in many businesses, including the 50/50 and now as Business Executive Coach help point a big flashlight on future success, the alternatives, the evangelizing and self checking needed etc. Not for the faint of heart, but hey, that is why you are the CEO. :-)

the start up is a quirky little animal. The most important item is to check for transferability to the buyer and scalability for future growth. Those two items, if strong, will increase the value of the company. Without them, well, not much of interest. I also like what Will said

such a massively situational item. Sometimes it is just obvious, and am assuming that the question is about those times when either way feel to be a viable option.
In that case, I'd look out a few years and the needs for when the venture is at least 10 times the present size. Do we want this partner, or any partner, or cash, or ... fill in the blank, at that future point? Answer that and the choice can become a little bit easier to see

most of the foregoing are spot on. Find the one that suits your style. No use putting the correct shoes on the wrong feet and then trying to run. The suggestion way up top about engaging a Business Coach gets my two thumbs up (yes I am a Coach) and I wish I'd have had the option when I was starting, growing, buying, selling and reviving my own businesses. One specific that can slip by is to avoid ongoing recurring expenses, things that self renew every month whether you use it or not. For the first while there are economical ways without that monthy cash drain out of the gate. Enjoy your business :-)