Which investors to present to seems like an odd issue to be having. Is it the particular investors, or the level of investor (how much capital, what level of experience, seed vs. a larger sum)?
I think when you get to the bottom of this issue, the others may solve themselves. For example, if you want higher caliber investors, your UI better be intuitive, attractive and fast - or you better have a helluva track record in turning an ugly idea into a winner.
Similarly, you can get additional engineer help by coughing up a little equity. No sense giving someone a salary unless you're taking on large amounts of capital, or have cash on hand. Which brings us back to the investment issue.
One of you wants to grow organically and one of you thinks the "win" is in getting a lot of venture money. You guys need to get on the same page with that and then I think the rest will work out. In any case, you should NEVER have to sacrifice in your vision of what the end product should be. Maybe a feature here or there, but you have the right to deliver on your vision.