I'd go for Frutescens.
Many are small when mature - Though some are monsters.
A lot are VERY hot but the heat doesn't last long.
Some I'd say are easily hotter than generic Habs.
Problem is you need to research the different ones - some are heat only,others are larger plants while others are hot,taste great and are great looking small plants.
I have several in 4 - 4 1/2 inch pots that are full of buds and podding up.
Some are only a couple (3+) months old from seed.
I'd guess your plants might get bigger in the Aerogarden than in soil.
A great one I'd highly recomend for looks and pod set would be CAP 1546.
Purple buds and pods start out the same color.Leaves are purple veined/dark green.
http://www.rainbowchiliseeds.com/catalog/i354.html
I see it listed ad a Frutescens and an Annuum.
So you decide.
Looks Frut. to me.At least my current plants.
I'm doing a Frut. grow.
Plants are just budding now and setting pods.
Will probably have isolated seeds soon.
Also will know how big the different ones get in #15 pots (5-7gal. - I think).