From what I understand, the Germans had the overall best optics, although it was pointless to have such good optics because fights were generally at under 1000 yards. I also understand that the US lacked a range finder for the gunner because he was supposed to be told the range by the commander. I also heard that the Soviets had bad optics early on, that needed re-calibration often, although I also heard that later they made some of the best sights. How much of that is true? How were the optics for tanks for the various countries compared to each other?
A variety of different gun sights was used by all major powers for different tanks and anti tank guns so its hard to say "best". The German tanks had several advantages when it came to gun sights.
Their newer tanks like the Panther and Tiger had gun sights which had adjutable magnifications which was very relevant since depending on the combat range they could adjust. Their guns allowed for long range combat so they had one setting for 5x magnification and one for 2.5 for smaller ranger combat. On top of that most German gun sights had a superior field of view which again allowed for better target aquiring. But don't forget different tanks had different gun sights.
Besides the overall specs of the gun sight the Germans used another technic which improved combat performance. German gun sights had an implemented stadiametric rangefinding which allowed German tankers to range the enemy target without a ranging shot which made it possible to get first shot kills. Being able to kill the enemy tank without wasting time on ranging is a significant advantage in combat.
A picture from the manual instruction for Tiger crews "Tigerfibel"
The triangles you can see there help determining the range to the target. German tankers had to "learn" the common enemy vehicles and their widht and lenght but they also had range tables. If you know these measurements for the target you can check them against those triangles. The triangles have fixed measurements. A Sherman facing you having the same width has the bigger triangle would suggest it is about 500 away.
The smaller traingles simulate an object which is 2m wide and high and 1000m away.
Here a picture from the book King Tiger vs IS-2: Operation Solstice 1945 showing the gunsights of the Tiger 2 Turmzielfernrohr 9d. Demonstrating the adjustable magnification. Noticed the mistake? The "triangles" didn't change which would indicate different ranges on the different magnicifation which obviously doesn't make sense. The tringle would regardless of zoom always indicate the same object on the same range.