There are so many varieties now and people have such different opinions that it would probably be impossible to give an objective answer about flower colors and designs. Maybe someone has a better answer about caudexes but arabicums can be quite large and dramatic...

I agree with Ted. If growing from seed, anything goes with 'obesum' as far as caudex, flower, etc. Seed grown Arabicums or Thai Soco's would most likely give caudex size, but not the array of flower colors.
If you can find or purchase plants and see them, then you can atleast choose what characteristics are your preference.
Rick