You won't have to worry about anything below a 3, unless you want to stay really far out. What are your priorities here? There are 6 SPG hotels in DC proper, ranging from levels 4-6, plus a level 4 in Silver Spring. Is location a priority? Do you want the best value, nicest overall, etc?
When I was in DC I stayed a bit farther out, in a Westin on the Virginia side of the area. If I was doing it again, I'd go for the Sheraton Silver Spring. It's really close to plenty of food and minyanim, plus free parking and a Metro station right there. It's also cheaper than the others (except for the Four Points, which seems like a silly idea once you're going to be in DC proper).
I think most people here seem to prefer to stay in the nicer hotels right in the thick of things. If you do too, I'd say +1 to the Westin Georgetown. It's walkable to the shul, 2 different Metro stations and to Eli's. Hard to beat that.