I believe both have their pros and cons. the split provides a feel of more rooms and space based on their layout. Colonials are very appealing and gives you a historial sense especially in DC.
I am not a realtor just a home owner <with a colonial> and yes to me it's nothing against splits it's just to me a colonial feels more like a "real" home to me. We moved from the split level to a colonial. We moved for the space but all things being equal I'd rather have the colonial. Just looked at the homes that my buyers did so far this year. 65% of them were colonials 25% were splits and the rest were a combination. Even one of the dreaded split foyers. I also think that what's reasonable for a neighborhood comes into play. Before we moved there were 13 homes on our street. 12 split levels built in the 1950's and one colonial built in 2006. It looked out of place to me and others as well. Nice home but I think he would have trouble possibly selling it some day also. Hope this helps just me thinking out loud.
A true split level is one of the most desirable styles (and my personal favorite). Traditional colonials are the most "standard". The only house type that I've ever gotten an objection to is a split foyer. Many families have told me to exclude those from their home search.
All in all, you should be in fine shape and as competitive as those Colonials out there. Buyers are most interested in condition of property, the amount of space, and the amenities the home has. You can't change the style of your home but you can make the home look amazing by staging and doing simple spruce up projects!