That's a really nice goal to do that before your 40! It reminds me the quote from Emil Zatopek: "If you want to run, run a mile. If you want to experience a different life, run a marathon".
I don't know all the marathons you mentioned but Berlin is definitely the biggest one with all the "big athletes". But I don't think it's not really important for you :)
Yeah, @toofasteddie was also saying that registration for London might be harder, so I'd guess the same goes for Berlin. This will make my options easier already. Do you have any tips in how I should prepare myself? Thanks!
I used to Zatopek program to train for my 10K and I believe it helped a lot since I improved my record by almost 10%. There is one for the marathon that you can download here http://www.zatopekmagazine.com/magazine/Belux/je-m-entraine-32/programme-marathon-13/
It's in french but it's easy to understand I guess.
Thanks I'll look into it.