It depends what your goal is? Do you want the fastest growing- Kohala, probably the most consistent fruited as well. Without knowing your growing conditions or goals, I would suggest Biew Kiew because it grows well here and has excellent fruit.
Same for Lychees. You should really try out as many varieties as possible to see which one you like best. You can try visiting the nurseries when the Fruit is in season to sample the Fruit. Mauritius and Brewster are productive here but a friend has a Kaimana that is fairly productive as well. Emperor is also a great Fruit and the tree stays small but it’s root system can be sensitive here in Socal. Sweetheart and Fake Hak Ip are good tasting fruit but they can have some tannin taste if you are the type to break the skin with your teeth.
All the varieties have tannin in their skin but some are more noticeable than others. Sweet Cliff is very productive as well with a smaller size Fruit, some people love it but it’s not one of my favorites because the Rose scent and flavor that I associate with a good Lychee is lacking in this variety.
Ohia is also a good tasting variety but I don’t know how well it grows here. Groff sucks from the few Fruit I’ve eaten. No Mai Tsze is by far the best tasting variety I’ve ever eaten. I don’t believe I’ve ever eaten a true NMT/NMC here in the USA.
Simon