The Fukushu handle low light better and can grow on almost any rootstock. The Meiwa taste better but are very finicky in doors. They can only be grown on a few rootstocks but many are grafted to bad or marginal rootstocks and grow poorly and/or die.

My fukushu on flying dragon

Fukushu on C35

Meiwa from seed

I have a fukushu kumquat grown 100% indoors. Very good fruit. Very prolific. If allowed to ripen fully they can be very sweet with a citrus/floral flavor very similar to a slightly sour mandarin orange. They are so sweet that I don't find them a good variety for anything other than eating off the tree, though they hold very well. I would have to defer to others regarding the meiwa, but I can answer any questions about the fukushu. I've had mine almost 3 years, indoors the whole time, and it's a monster of a plant.

Generally among people the Meiwa is normally thought of being the sweetest.

I like Indio Mandarinquat. Also quite easy to grow. If you like kumquats, this fruit really packs a punch!