I liken it to the mates you grow up with compared to mates in later life.
I talk to my mates now about all sorts of issues and seek advice. I've been on weekends away with them more than my growing up mates and would confide in them now before my old mates (I moved away from mcr at 21).
I'll always remember my old mates more fondly though because the first time I went to high school, the first time I kissed a girl, the first time I got drunk was all with them and some of those memories can never be replaced.
Nostalgia and longing means some people (including me) will never prefer the Etihad over Maine Road regardless of how many great days we have there.
I felt like Maine Road was mine somehow. I never worried that I wouldn't get in, never felt like I'd get in any trouble. The 5-1 derby is etched into my memory, the bananas, the Wigan play off game, the Birmingham Friday night match a year later, Liverpool at home when White scored twice, Niall Quinn's penalty save, sending Sunderland and their horde of fans down, the "Red Devils" parachute team being roundly booed off the pitch prior to the first ever Monday Night Football against QPR, the Kippax last stand against Chelsea, trying to get out of a Kippax tunnel after an FA Cup win against Barnsley and the noise echoing, deafening, Tottenham blitzing us in the quarter final when we thought it was our year, Oasis blowing the lid off on consecutive days, the feeling of despair a week later when we went down, the bloke who streaked against Bury and got one of the biggest cheers of the season, getting two buses straight there after being kicked out by my Dad and buying a ticket for an away match that I couldn't afford, the air of optimism after annihilating Blackpool on the first day in Division 2, going into the final season knowing the end was near, the last derby being one of the best atmospheres ever and then the weird feeling on the last day knowing when you walked out - you'd never walk back in.
If a genie gave me 3 wishes, I'd have the ability to pull whatever money I needed out of my pocket, eternal happiness for my family and then players such as Aguero, Silva, Kompany, Yaya, Zabaleta, KDB and Fernandinho to run out in front of a packed Kippax Street Stand to the roar of a terrace full of blues including yours truly.