Since you don't know what variety you have in either case--the green sweet bell or the chocolate bell--you could have an open-pollinated or a hybrid and seed may or may not come true to type. You won't know until you plant the seed, grow it out and see what you get.

Pretty much any bell pepper variety I've ever grown here has produced well, so you can just choose the size and color you want to grow. Bell peppers that have produced especially well for me in the past include Blushing Beauty, Roumanian Rainbow, Vidi Crimson, Lilac, Golden Admiral, and Valencia. I generally don't harvest any bell peppers in the green stage because their flavor is so much better if they are allowed to mature to their full ripe color.

For a really large pepper, you cannot go wrong with Super Heavyweight. Chinese Giant is another very large bell pepper, as are Whopper, Goliath and Big Bertha. You can read descriptions of the various pepper varieties at the websites of Totally Tomatoes or Tomato Growers Supply Company.

FYI--most people who grow their own peppers sow the seed indoors about two months before their transplant date, raise the seedlings indoors, and transplant them out into the garden after all danger of frost is past. If you direct seed peppers in the ground now, you will not be harvesting many peppers until fall. If you plant transplants now, you could be harvesting in June or July.

The OSU-recommended planting dates for peppers are April 10-30 (for earliest production) or later (for succession crops or for later production).

I've linked the OSU list of Recommended Vegetable Varieties for Home Gardens for you in case you're interested in seeing which ones they recommend.

Here is a link that might be useful: Recommended Vegetable Varieties for Oklahoma