I have never been a fan of carambola until recently. I have been picking the fruit at maximum ripeness stage, from Excalibur's trees, and have found the following:
Bell - moderately sweet to sweet, least favorite, had a bit of astringency though by cutting off the skin that dimished
Kari - very sweet, tropical citrus flaors, strong/intense flavor (for a carambola)
Sri Kembanqan - very sweet, tropical citrus flaors, strong/intense flavor (for a carambola)
Hart - sweet with a different spectrum of flavors, not as intense flavored as Kari and Sri Kembanqan
As I stated above, these were all picked with full ripe color, very little to no green color left. When picked like this they must be eaten fairly quickly but it was well worth it. At this ripeness stage, they would be excellent chilled and put through a juicer.