First off, since you didn't say what kind of shark you're riding, are you looking to replace footpegs with floorboards, or are you looking to swap your existing floorboards for something different? If it's the latter, keep in mind that you can just get inserts that will replace the stock HD rubber instead of replacing the entire thing (this is handy if you're on a budget).
With that being said...
Probably the most important thing for passenger floorboards I would say is: will it support your passenger's entire foot (or at least most of it)? Keep in mind passenger floorboards are typically about 1/2 - 3/4 the size of the driver's. Since MOST passengers are probably going to either be women or children, this shouldn't be too much of an issue, but considering I was wearing size 13 shoes at about 12 years old, it could be an issue for some.
Another thing to consider: how far out from the bike will they stick (even when folded up)? This can affect how easy it is to walk/back up your bike.
Other than that, since they don't really affect performance, the only real concern is aesthetics... does it look good to you? Personally, I would start by looking at the bigger names in the aftermarket accessories first (e.g., Kuryakyn, Arlen Ness, Performance Machine, Show Chrome, etc). If, however, you don't see anything that catches your eye, start looking at some of the other brands.
Good luck, welcome from West Michigan, and congrats on the new ride!