Hmmm. Very open ended question. What you should do is take a look at a style you are interested in getting at least. If you can find a local airsoft store and pay them a visit. That will give you a direction to go at least.
And "Door to Door Combat" isn't really a good term. I'm guessing you meant "Close Quarters Combat". Again there are many airsoft guns that will work in this role.
when considering a CQC weapon for airsoft you dont necessarily need to consider a lot of the same aspects you would for a real world weapon. only a few.
in fact... only one. size.
weight between airsoft guns is negligible. your only true obstacle will be navigating these scenarios with your weapon in an 'at ready' position. however, due to the extreme light weight of most airsoft weapons, and the complete lack of recoil, you are able to hold and fire the weapon in many non-traditional positions and still fire effectively, such as blind fire around corner, at the hip, hell, you can fire the thing with stock on your head.
that being the case, you only need to steer clear of rifles in the M16 size, which imho are perhaps too large for general play (depending on rules and if you play with disabled weapons or not) because the benefits don't outweigh the cons like with a real rifle. so, that being the case, dont feel obligated to opt for the H&K MP series simply because its what the navy uses for CQC. i have an M4 style gun with a full stock (not the adjustable) and i have yet to be in a CQC scenario i was unable to tackle effectively. perhaps im unique, knowing full well during my purchase that the stock would never leave the fully extended position, i opted for the full stock to use the full size battery.
the only other aspect i considered during my purchase was the guns my teammates where using. i was playing with a fair sized group on a regular basis so i decided to purchase a gun that would allow me to borrow and lend mags to my teammates. as apposed to getting the G36 that i wanted, and being the odd man out, i went CAR15 variant, and am verry happy i did. not two games after my purchase i was stuck in a bad spot, i had just dropped my last mag and ejected all the BB's onto the field. all i had to say was im outa dog food and i had two or three mags thrust in my direction.
in the end it really comes down to personal preference. come back when you know what type of gun you want and ORCA will give you a list of appropriate manufacturers, im sure.
usually you want an automatic of something that shoots many rounds. i.e. shotgun. you want something that is reliable, durable, or has a warranty. For example: i have an SD5 airsoft gun. had it for 3 years. hasn't broken and has good accuracy and range. its not really about the best gun, just the gun you're best with.