Formosae type is one of the easiest to grow, but you have to pay a little more attention than nobile type. You can not totally neglet them like nobile type, but they are totally worth it. The flowers last twice as long as nobile type and huge too. Most are warm to intermediate to cool grower, depending on the species and what you can provide. They need bright light, even watering year round (more during active growing period) and need a very short rest (1-3 weeks) after flowering. The size can be vary from 2-3" to up to 3 feet too. Most species grow anytime of the year and flower from spring to fall, and they don't really have distint growing season like nobile type dendrobium. And most bloom as soon as the new cane mature or shorterly after, at least from my growing experiences.
Warm: 16-17'C min
formosum, deareii, schuetzei, cerutum
sanderae (& its variety), draconis, williamsianum, trigonopus
infundibulum, bellatulum, christyanum,
I think these are the easiet to grow from the formosae group and probably the easiest to find. There are other species like lowii, longicournu, virgenium, etc. but they are either a little harder to grow or hard to find.