The Danforth-type anchors have been king in the Chesapeake Bay and its tributaries for over 50 years. They still are, IMHO.
I'd go for a Fortress anchor. Very light, very strong, and perfect for the lower Potomac area. The 4lb Fortress is rated for boats to 27' or so and can be had for under $100. But, I'd probably go for the 7lb Fortress which gives you a LOT of safety factor for anything you're likely to encounter.
Check out prices on eBay, e.g., Fortress Anchor FX7 | eBay