The key is to add the important features Pete mentioned, keep them functional and easy to use, and keep them out of the way. Space is always a premium and you need to keep your floor space intact, not overly crowded. This helps when your fishing 3 people.
Storage is another very debatable subject. The only storage compartments I like is a front seat compartment. Your passengers will sit on this seat box. Lots of storage without sacrificing floor space. And I also prefer some storage under the rowers seat. I use this as a regular tackle box and gear storage. There is also a slide out fish box under the rowers seat, I like to keep my fish hidden from view.

What I don't like is the transom mounted storage compartment, unless, maybe your fishing a very large boat, like 18 to 20 feet. I'm just guessing here since I've never owned a large boat like that. The rear floor space near the transom can be used to fish from, stroage compartments can reduce and/or eliminate this space. I often use this space to provide better seperation between fisherman. Longer boats have more room near the transom, appears these boats can accomodate a storage box and seat for an additional person. Check the transom floor area and see if you can stand up here. The next stoarge option is the front bow compartment. You certainly can stuff a lot of gear here. Except I like to run a heater under the front deck, making a compartment impractical. I vaugley remember seeing a slide out drawer that looked pretty cool under the front bow deck, anyone have one and how do you like this?
When you start looking around, you'll see drift boats layed out in various arrangements. The biggest variable is storage or lack of. If a boat looks cluttered, then it probably is. Every piece should be functional and well designed. The manufacturers can help with your selection, ask about each option and it's intended use. Some options are trade-offs, like storage compartments, some people don't mind sacrificing floor space for a storage box. The manufacturers have seen it all and can explain the intended purpose of each item.
On that note, it's also important to figure how your going to use a drift boat and the number of people you'll regulary take out. Also, don't forget to ask about motors, drift boats are versatile and can fish many locations.
Don't forget to search the IFish archieves, lots of good information located there.
best of luck,
Gregg