Tier 8 Tiger II / King Tiger
Went into a training room with two Tiger II's for both of us to get a better feel for them. He had the shorter 10.5 barrel, and I had the longer 8.8 barrel (so neither of us were fully upgraded).
At 150 yards the results were hugely disappointing considering that neither of us had the gun that most tier 8's will be using (that has 225 penetration).
No matter how we angled, all but the most ineptly placed shots penned the lower and upper glacis, as well as the turrets. Shots too close to edges didn't pen, but otherwise... in three training room sessions we came away with no real angle, from 5% to about 40%, that helped on the fronts. Unless there is something special in the penetration area with the KT's lower tier guns, I'm not yet seeing the reason to run it vs. a Panther II on the battlefield except to have the option of eventually bringing a much bigger gun.
Tier 5 M7 MT
The American M7 tank: I always wanted to like this tank, and it does have some lovable qualities... but I still feel that something is off with its balance. My guess is that the gun is too weak.
But I bought it again yesterday for the x5 event since this seems to be the tank that the new American line in the upcoming 8.2 patch will take off from. My initial guess is to work up about 25,000 XP with it to have it close, or ready to go, to research the new tier 6 when it comes out.
Tier 4 A13 Covenanter tier 4 British Light Tank
Only after having researched all three "upgrade" guns on it, and trying them all, did I realize that the stock gun is best. I don't need a two-shot / two-load auto-loader where the second shot always misses unless I'm right up against a target, and I certainly don't need to "upgrade" to 63 pen from 78 original pen, more accuracy, and less gold rounds wasted (gold rounds for x5 victories are a staple in my tanks' diets)
The HE "upgrade" gun is crazy, too - it's as if the round, when fired, enters a different dimension, then comes out at the other end a few days later. I played one game with it, and was shocked at how much slower the HE round traveled than even other tanks' HE rounds. After a few missed shots where I greatly underestimated the round's travel time, I took a shot at a damaged PzIV off on the distance, but then gave up on and moved away... only to hear I killed it like... a day later? My buddy had the same bad experience in that he took a distance shot at an enemy, but by the time the round got there sometime the next day the battle had changed enough that he killed a teammate instead.
I don't really like the Covenanter, but I'm choosing this more forgiving tier to hold on to the tank, and elite it (soon), to train the crew up to 100% and get them some perks before moving on to the much more competitive tier 5 class.