I saw the TV ad for Aces High and joined shortly thereafter (in late 2007?). Advertising pays.
That said, I left AH after only a month or so. I found out about Warbirds around the same time, tried it out and chose Warbirds over AH, cancelling my first AH subscription then.
Why did I choose Warbirds?
Two reasons: TRAINING and COMMUNITY. I felt (and still feel) that Warbirds had far more accessibility to Trainers and that allowed me to learn at a much faster pace. Realistic flight sims are HARD and without help I probably would have quit (getting your butt handed to you without understanding why for several weeks on end wears on you.) At the time, WBs had at least 3-4 trainers MINIMUM on during set hours (one or two nights during the week and one weekend time-frame) that were meant for new players to attend. New players always had priority over experienced players and experienced players in the Training Arena were expected to help the trainers out. In my opinion this focused on new player retention and it worked on me. I don't feel AH is as aggressive with that process.
In a more general sense, WB's seemed at the time more of a "we" community, with lots of people willing the help. Whereas from day one, AH seemed much more like a "ME" group. Warbirds was not as good of a game, but I chose it over AH for the reasons stated. As the game felt more and more outdated, had increasing problems, stagnant arenas with and lower and lower player populations (sound familiar?), I left. I then gave AH another go. After (finally) getting some training and being invited to a squad in AH, I stayed.
My point in all this, for all the people who complain about arena pop and player numbers, I ask: How often do you specifically seek out new AH players (based on their stats or actions) and offer to take them into the TA to help them? How often do you go into the TA to see if anyone new there is looking for help?
Sadly "shading" seems to have a long tradition and be a fun past-time in AH, which perhaps discourages this. (I never ONCE heard the term "shade" or accusations of shading made in WB). Personally though, I'd rather make the mistake of asking a shade if they need help over potentially losing players to the indifference (at best) and abuse (at worst) that many AH players dish out to new people.
My two cents.
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Ryno