I agree with Brian, just tasted these kumquats in the last week or so.
1. Nagami
2. Nordmann
3. Meiwa
4. Marumi
The Nagami and Nordmann tastes indentilcal but the Nordmann has larger fruits and was seedless. I ate the Nagami from two different sources (friends trees), and the Meiwa is from my grafted tree.
I'll find the photos I took and post it later for you. The Marumi fruit I tasted with the others again at the UCR/CCPP grove (Research grove at Riverside).
Of these 4 kumquats I ate, the best tasting (sweetest) was the Marumi.