The T-26 may have been an excellent design in the early 1930s, but was hopelessly out of date by the time it entered WWII in 1941. That may make it a good tank, but NOT a good "WWII" tank. The BT series was either too heavy for a "light" tank, or too light for a "medium" tank; its performance against German medium tanks was notably bad, probably related to crew training, operational doctrines, and other issues not related to the tank itself. I've seen photos of abandoned BT-7s scattered across a field with the twin top hatches standing open, giving it the nickname of "Mickey Mouse". Use of the later T-60/70 light tanks was similarly inept for the most part, and overshadowed any possible merits of the vehicle itself.
The Panzer II was envisioned as being a "general purpose" tank, while the heavier Mark IIIs dealt with opposing armor, and the Mark IVs delivered HE where needed to support the infantry or suppress AT emplacements. In that role, the PzKw. II was very adequate, but nothing spectacular, until the increasing weight of anti-tank firepower on the battlefield made it too vulnerable. "Schwerepunkt" tactics relied on the heavier tanks at the front of the formation to absorb most of the AT fire, essentially "armoring" the lighter vehicles until they could bring their firepower to bear effectively.
The Panzer I was relegated to training and anti-partisan duty fairly soon after its introduction, and many were converted to command vehicles or SPGs of various types. That's not what I would call a "best" light tank.
The Czech "38" model (I don't know the Czech designation, only the German: PzKw. 38(t)) was a particularly commendable designs. In its various successful SPG variations (Marder, Hetzer, etc.), the Czech chassis continued in production for the entire war, so that has to speak volumes for the soundness of the design. This has to be a serious contender for "best" light tank of WWII.
The Polish 7TP gets little attention, despite a fairly solid performance under terrible circumstances. I don't know enough details to comment further.
The Italian Ansaldo CV-33 saw service from 1935-36 in Ethiopia until 1942, when Hungary replaced the last remnants of its purchased Italian "training tanks" in Russia, where they were reluctantly deployed because their domestic Toldi and Turan tank programs were unable to provide enough vehicles in time. By that point, the Hungarians recognized the true value of the tank, instructing the crews to bail and run if enemy tanks were sighted, rather than stay in the vehicle. It may have been a solid tankette design, but was a pitiful excuse for an actual tank.
The Swedish (Landswerk) designed and Hungarian upgraded Toldi I, II, and III light tanks served in both Yugoslavia and Russia, and were claimed to be solid and effective while they lasted (most were operated long past their rated operational life). Adequate, and roughly comparable to the Panzer II in many respects, but a couple of years too late, so not a "best" design.
Then there is the American Stewart. It was heavy for a "light" tank, but its armor made it tough enough to use for infantry support work. The high profile made it more vulnerable to AT guns and other tanks, but also gave it a better line of sight and fire in return. Overall, I'd rate it very highly for its performance in its intended role.
I've seen pictures, cut-away drawings, and specs on the Japanese tanks, but little in the way of information on their actual performance. I can't rate them.