This is an ultra tricky proposition as there can be many moving parts.
Personally, I'd start with the basics and look for an accountant that can fulfill your Accounting 101 needs. The reason for this is that when you first start a relationship things can sound really good, but the real proof of performance is evident at crunch time. Whether filing quarterly statements or year-end taxes you'll know quickly if you made a good choice in accountants. If they can fill your basic needs then you can talk about more advanced options down the road.
Any good accountant can help you setup your books, the better ones help you plan for the future. If your future includes rounds of funding and a potential IPO that's great, but you'll discover that requires a team of accountants plus more than one attourney. By starting with a basic accountant you'll be able to ensure your books are ship shape when it's time for some heavy duty financial maneuvering. Plus, you'll only have to pay basic accounting fees early on when money is tightest.
If you take the other approach and hire on a heavy hitter from the get go you'll be locked into high fees, stock options, or even a CFO position. What if it doesn't work out, how do you unwind that mess? It's a very high risk proposition. Plus, there is a good chance that new investors will already have an accounting firm in mind that gives them peace of mind that they will want to use. So it's better to take baby steps while you learn the lay of the land.
My oldest business is 14 years old and we've been through 6 accountants. Everything can go great until they: get pregnant, change firms, move away, become too busy, etc. The landscape can change quickly and it's best to keep your exposure to a minimum.