It depends entirely on a tank and it's gun. Some tanks feel nice and comfortable everywhere (read: they have balanced gun), while others suffer when thrown at higher levels.
Example: german tanks Luchs and Leopard. Luchs is a 4th level tank with 95 pen magazine machine gun and meets tanks from level 3 to I believe 7, but mostly 4 to 6, where it's machine gun with average alpha of wtfwhat 300, more often between 200 and 300 can put holes in almost anything, and of course level 3 and 4 tanks just explode from this sort of fire power.
But then take Leopard, it is a higher level light tank, which is huuueg and with same gun, but it gets thrown at even higher levels, and no level 3 or 4 for you, so you have same gun, with 2 more bullets, but now you are out of your "comfort zone".
There are other examples like L/70 or Waffe that you can get at level 5 tanks and keep at level 6 tanks and be OK, but then they make you use those even at level 7, and now it kinda sucks.
tl;dr for me it's all about tanks that are in a "comfort zone". This means guns with good pen combined with good mobility. Examples of those on my level are VK3001(D), T34-85 & Cromwell tanks.
Ofc if you just want to shoot anywhere and pen anywhere you can try TD but, the paradox of this game is: gun is everything, but gun is not everything. For example, Pz. Sfl. IVc aka Coffin aka Barbecue has a 194 pen, 240 damage anti air gun AT LEVEL FIVE... and so what? It's hueg as fuck and you can't shoot for shit in this thing cause gun doesn't rotate at all.
Personally I find TD extremely dull and anything without turret to be dull. But I guess you can always praise amurika and get yourself a Hellcat and enjoy.
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The amount of pen you really need in the game is actually lower than one might expect. Everyone wants to shoot at front and kill but truth is some careful aiming will take you places. Not everything can be killed by raw pen. For example, british tortoise-series can only be taken down by careful aiming, as well as tanks like american T29 (which is a glorious looking GDI mammoth tank and probably will be second tree I am going to explore).