The 3601H maxed out is an excellent tank, provided you use it properly. It is a medium tank that has nearly the armor of a Tiger, and has the short barrel 88. It's fairly quick, and agile. That 88, used correctly, hits most tanks hard. I have one, maxed out. I also have a PzIV maxed out. The 3601H is a better tank, but it draws more attention because it is more feared. The PzIV for me actually has the best performance percentages of all of my tanks, probably because I use it better than the 3601H or the Tiger II. If I used the 3601H more like I use the PzIV, it would easily meet or exceed the performance standard set by the PzIV.
I only bought the PzIV in order to grind to a Hummel. I was surprised by the fact that the PzIV gained credits and experience so rapidly that I was able to max it out and get the Hummel very quickly. I had intended to sell the PzIV as soon as I bought the Hummel. It's staying in my garage, it's a keeper.
If you can't do at least fairly well with a 3601H or a PzIV, you're playing it very poorly. Even I can do fairly well with either, and I'm a horrible player.
The first thing you need to do when you purchase a new vehicle is spend the 20K credits per crew member to move to the 75% training level. The gain is obvious, they will do everything better, and once they get to 75% they perform enough better that they progress rapidly from there on. I often spend the 200 gold to get the commander to 100%, because the crew works better under the 100% commander, and gains their experience faster as well.
When you purchase a new vehicle, you need to have around 200K or so credits, at least, to spare. I prefer to have 300K or better. I'll spend up to 120K to train the crew, and then I'll get every upgrade that may be already researched.
There are tanks in the trees that are only purchased because you have to move past them to get to a good tank or other vehicle.
Avoid auto aim. If you do not know already, auto aim will aim for the center of the plan form presented to your sight. If you are looking at the front, it aims at the thickest possible armor on the tank, usually where there is plenty of slope. A complete waste of a shot unless you're shooting a long 88 at either an artillery piece, a light tank, or a light medium. If you're looking at the side, it'll aim for the base of the turret. Again, unless you're over matched on him, it's likely to be a complete waste. If he's peeking out from behind an obstacle, you'll hit the obstacle. Again, a complete waste. If you're looking at the rear, it will often shoot the base of the turret instead of the engine, another wasted shot.
If you're playing an artillery piece, even if all you do is track the enemy, not only are you racking up damage credits, you're immobilizing him for your team mates. With a decent shot, any artillery piece can score a one shot kill on any other artillery piece. And your first job as an artillery piece is "counter battery". Find their artillery and kill it. It keeps them from killing you or your team mates, and once you do that, so long as your team mates do their job and keep the scouts away, you can wreak havoc on the opposing team. I don't even want the big gun for the Hummel. It's too slow to load and too expensive to shoot.