as an avid car buyer and one that too has trouble keeping cars for very long...I can say this. Try to enjoy what you have when you have it. If you do not enjoy the M3 then you may not enjoy that type of car small-midsize sporty and fun. It is a great car. AMG's are different especially depending on which type you are talking about. closest comparison is the c63. The E 63 is so much larger and just different especially for regular driving. If you like more cruising and comfort and occasionally want to "get on it" or do a sick burnout then E63. Just my opinion. I have had them all and they are all great in their own right, at the end of the day it would be nice to have ALL of them, but in the meantime try to enjoy what you have when you have it because they all come with compromises of some type and greatness of some other type.
D

 

I was in the same boat as you. I was looking between the M6 and the CL63 AMG. I ended up going with the CL63. The benefits of the M6, however, were the fact that they covered everything! You literally don't have to pay a dime in service where Mercedes charges you for everything. I am also young and understand your mindset. I thought the AMG was much more practical as a daily driver. Yes, the tires are an issue but I just threw some wheels on with harder tires (Pirelli). Problem solved (for the most part). If you don't mind paying for the maintenance, I would definitely take an AMG. If maintenance will be an issue, then stick with the M. They are both fantastic cars and you really can't go wrong. The C63 and the E55 are awesome cars. I think the E55 is more comfortable and looks beautiful. The C63 I don't really love, but it is stupid fast. I would go with the E55 over C63 & M3.

 

If maintenance costs are a factor, you probably shouldn't be looking at this kind of car. Even BMWs will be expensive to maintain in 4 yrs.