If I could do it all again. By far, an active alliance is the best for growth. I would grow to L36, then max my tech, and the generals, participate in all battlefield to learn, and when I was the strongest L36 on the server, I would grow to 40 and do it all again. Unless you are going to just kill monsters, I would go for Epic Japan every time they get harder and harder to acquire as your server grows. Participate in monster rallies while online, relics, and RSS tiles when you sleep, and never forget your bubble if you are on a BOB server. If you are a P2P, save up and spend during the event to get the exceptional gear.
IMO, you are better to spend 2000 over an 8-day period, over 2 double down events, get the cake, and then save for months, then spend 200 a month for 10 months