Okay, I'm going to say what everyone else thinks. The E-100 is the better of the two.

First off, you are more maneuverable. Sounds funny considering the E-100 isn't the quickest thing around, but it sure is much faster than the Maus.

Secondly, your armor is much more reliable in the E-100. This also sounds odd, due to the Maus being a very heavily armored tank all around. It has the armor, but not much sloping at all, which means at tier 10 it's armor is kind of useless against the high penetration guns it comes up against. The E-100 has sloped side armor too (Not all of it, but it has a very prominent curve at the upper part of the hull side). The sides and rear of both tanks turrets are both as terrible as each other - Flat and not very well armored. The difference though is the front of their turrets. The E-100's is flat, but this means it can be angled which makes it much more effective for bouncing. The Maus' is quite bad, tier 9's and a good amount of tier 8's should be able to get through it head on.

The front of the hull on both tanks is great, but only if they are hull down as the downfall on both of these tanks is the frontal lower glacis. It's much worse on the E-100, with it spanning across the whole width of the hull, whereas on the Maus it's actually rather small and sometimes very difficult to actually put a shot into.

The guns are the questionable difference on which is better. The Maus gets the 12.8cm gun on the E-75 whereas the main armament on the E-100 is the monster 15cm gun (Although you can still use that 12.8cm that the Maus gets on the E-100 as the 'stock' gun).

Now both have their advantages. The 12.8cm on the Maus is a faster reload, more accurate, has better penetration and does 490 average damage per shot. The 15cm on the E-100 has a long, 15 second reload (With certain perks + Equipment), is less accurate and less penetration but has a monster average damage of 750. This factor kind of seperates the way they should be played. The E-100 is definitely a brawler as it needs to cover up weakspots but be close enough to hit the enemies' weakspots due to the lack of accuracy and pen. The Maus is more of a close-medium range fighter due to it's lack of mobility. It needs to hang back just a little so that it doesn't get overrun holding a corner, which can easily happen with it's slow movement.

Finally, the one thing (I feel) the Maus has over the E-100. Hitpoints. The E-100 has 2700HP (Which is still a massive amount in itself) whereas the Maus has a whopping 3000HP.

Both tanks are great in the right hands, which is not often seen due to people not understanding how these machines work. But I also feel that the E-100 just does everything a lot better than the Maus, but that's just me.