Modified repost following October, 2018 server failure...
Now in stores: The first line of retail LEGO sets specifically meant to make spinning tops (as opposed to other spintoys). A set making one complete top with ripcord and grip goes for about $10. These Ninjago "Spinjitzu Masters" (SM) tops perform quite well as both ripcord
and finger tops. Decent value, very sturdy, and lots of fun.
Challenge: Members of this forum will no doubt get SM tops to do things never imagined by LEGO. Would love to see some videos!
NB: Don't confuse the SM top with a similar LEGO spintoy line also in stores -- the "Airjitzu flyer" (AF) series. The AF spintoy certainly functions as a top after landing, but it's primarily made to fly and marketed as such. SM sets, on the other hand, are optimized to function as tops -- mainly by increasing rotor mass and rotational inertia per unit mass. The visual similarity comes from the fact that SM and AF spintoys use the same clear dome, same black hub+tip, same ripcord, and some of the same minifigs.
Renee reviewed an SM top in a recent video (now lost). My own take...
1. Unmodified SM tops perform well as both ripcord and finger tops. No AF top comes close on either front.
2. Ditching the minifig under the dome improves performance in both SM and AF tops. Without minifigs, my SM tops stay up ~40-45 s by finger twirl and ~10 s longer by ripcord. By comparison, my AF tops stay up ~20 s at most.
3. The dome is optional in modified AF tops but turns out to be the best-peforming stem in all cases. Impressive launch speeds can be had with a twirl of the fingers on the dome. The dome's mass distribution also slows spin decay.
4. Other than the colors and minifigs, very few ways to modify AF tops without destroying top functionality, and
none that I can find for SM tops.
The modified AF top below replaces the minifig and dome with the LEGO stem I tend to prefer in other tops. It stands only 10-12 s by finger and under 20 s by ripcord. As with SM tops, nothing you can do about the tip.