Maryland is a good climate for growing peppers. I'm next door in Virginia - it might be slightly warmer here, but not enough to make a huge difference. Peppers really dig the warm but not scorching summers here.
2 1/2 gallon pots are really not sufficient. You'll get "something" out of that size, but it'll be seriously deficient in pod size and quantity relative to using 5 gallon pots. You just have to ask yourself if you'd be happier with a plant with 50 jumbo pods or 2 plants with 20 small pods each. Bigger pots are better.
Given that we have about the same climate, you'd probably find the same ones easy to grow that I do. First and foremost, Jalapenos, specifically the Jalapeno Early. A bit hotter but also super-easy to grow are Serranos. The easiest of all for me is the orange habanero and the aji amarillo, each of which produce 100+ pods for me (but the ajis are very late season, and the fruits of your labor won't be ripe until mid to late September). Actually, all habs grow well here, but the orange habs are just bulletproof; they start early, produce continually all the way through to October, and I'm literally handing out bagfulls of them to neighbors in September for lack of any way to use so many pods. I recommend orange habs if you're looking to get something easy and fulfilling going.
Even MORE prolific and easy to grow than the orange hab is the "Hottie". These are sort of a "new and improved" hybrid version of the orange hab. These are just unstoppable - 100+ per plant in pots, about 1.5x the size of orange habs. They're disease resistant and seem to produce with or without fertilizer or regular watering or any amount of sun. However, they are not quite as flavorful or rich as the orange hab - a bit more bland. But easier on the pallet of folks who are not used to habanero-level heat. More of a serrano-class heat, perhaps. Stink bugs love these, though - if you have that problem in MD like we do in VA, just know in advance you might be donating half your pod count to the Bug Gods.
