I would advise the american line. It has some of the most maligned tanks, but some of the best. The M3 Lee kind of gets a really bad rap, but its front armour is dead tough and it has a fantastic gun. Just play it more like a TD and you are fine.
The M4 and E8 are great as I said.
From there you can go along the american Medium Line for the Pershing and Patton, which are pretty nice high tier mediums, or the heavy line.
The american heavy line is rough, the T1 Heavy and the following M6 are huge, enormous targets with weak side armour, but after a while I grew to love them.
After the M6, you get rewarded for all of your pain and being told you suck for choosing american with the T29. The T29 is an absolute monster in its tier with an amazing, fast firing high penetrating gun and decent armour. Get an american heavy in a hull down position, and it cant be beat.
After the T29, the higher tier american heavies are kind of so so. They are generally all gun and little armour, but have good mobility for their size. The Tier 10- The T30, is actually a giant TD.
There is an update to the American tanks coming, in which anyone who owns an american T34 or american T30 will keep those tanks, but have the moved into new spots (The T34 is going to be a cash bonus premium like the Lower and KV5, and the T30 is going to become the tier 9 TD of the second line of American TDs). When those tanks get moved, the players having them will also get a bonus tank- the tank that is taking their original spot will be given to them for free.
The same goes for the KV, KV3 and IS4- the IS4 is going to be upgraded to a tier 10 along the IS7, and the KV is being split into the KV1 and KV2.