A little update on my findings in case anyone cares...
Early Jalapeno: Very small plants. Produce small peppers for me, which seem to show some decent corking and look pretty good. But everything about these plants scream "is there something wrong," because the peppers rarely grow over an inch long and have a small diameter at the base, and some are pathetically small (as if their average size characteristics aren't bad enough...). The generic "Jalapeno" plants must be Early Jalapeno plants, because they have nearly identical traits. Peppers mature to an attractive bright red and have a very good flavor, as well as acceptable heat. They ripened early, as advertised. They'd be awesome if I could just get the plants to grow well and with bigger peppers... maybe they're just picky plants. Anyone else have trouble with this one? They're supposed to be as big as the Jalapeno M, but they're nowhere close. They remind me of serrano peppers in size.
Jalapeno M: Pending a taste test and close-up examination, as the fruits are not ripening yet. Much bigger than the Early, and nicely corked, but not near as much as the BBs. At least, not the last time I looked...
Biker Billy Hybrid: I love the looks of these. Very nice size to appearance ratio; not my biggest jalapenos, but certainly of good size and shape in general. Look really good with lots of corking. Mature to a darker red than the Early Jalapenos. Flavor, IMO, is not as good as the Early... but the heat is certainly higher. Overall, if this pepper turned a brighter red like the Earlies and had the same flavor, IMO, they would be perfect. The darker shade of red still looks pretty good though. Relatively early ripening, comparable to the Early Jalapeno in my case.
Mammoth Jalapeno: Meh... hardly any corking at all, they just look plain and ugly. They are, by far, my biggest jalapenos though, and growing on a big, sturdy plant. One pepper is finally turning red; I'll probably find out soon where this one stands in terms of flavor and heat. But unless it's awesome in both aspects, I probably won't grow it again... I'm just completely unimpressed with its appearance so far... too smooth and boring.
Mucho Nacho: I'm growing them, and to be honest, I haven't been paying a whole lot of attention to them. Been busy with my chinenses and mostly attracted to the Biker Billy plant. I just remember they're small, but longer than the Earlies, and also on a small plant. The plant is shaded quite a bit by the garage compared to most of the rest.