I have seen a Carambola tree around 60-feet tall. What a mess it made!
My favorites are Sri Kembangan, Kajang, Fuang Tung, and Bell. The flavors and appearances are distinct enough to merit having all four. The Kajang and Fuang Tung are very delicate and short shelf-lifed.
If you manage them as shrubs, where every fruit is within reach of your hands, you can have three or four shrubs in the space that most people let one tree take. So start with 3-gallon trees, not 15-gallon; you will be way ahead.
B10 is respectable, and more flavorful than Arkin. These are selected for commercial packing-house toughness and shelf-life.