I have owned the DL and the Area 51....no firsthand on the other engines. Both have moved on to good hands as I moved up to 150cc.
Speaking of DA....I like all kinds of engines but find the newcomers trying to give, "DA Like Service." We all know that DA has set the industry standard and that is good for us modelers. The DL service I experienced was good. I took a picture of the cracked muffler and they sent it the next day while I mailed in the defective part. I got the same out of the Rc ExtremePower gang when the Rcexl ignition went out early in the game....only this guy work's weekends. My problem happened on Sunday afternoon, by 10pm I had exchanged two emails and he had a new unit out Monday morning.
It may make it sound like the engines were not very good, but to the contrary they are good engines for the price. The Rcexl ignition is used in a lot of engine brands today (including these two) and I treat it as a fluke, one in a hundred...happens. To me the muffler problem on the other was an early issue that likely has been resolved. That muffler was pretty darn light, going for all out broke in the engine weight wars I am sure.
Both engines right out of the box (Area 51 has a prettier box
) easily cranked up. The DL took some carb priming, normal for a brand new engine. The Area 51 popped on the second throw and when the choke was off, ran on two more flips. After flying, whether you sit 5 minutes or an hour the 51 was a one flip restart. The DL might be two or eight and had to be choked if it sat until cold.
On running, both will idle well and transition well too. The Area 51 has a mid range that is "Smooth as Silk," and impressed me the most. No noticeable gurgle that the DL had. It also impressed Chris Hinson when he went to China to fly an EF prototype with that engine on it. By the time he came back to the states he had picked up the line and now sells Area 51's,
Top end on the DL after several gallons would turn around 6800, after 5 tanks of gas the 51 was hitting 7k on the same Vess 23A. Reports are that when broken in they get nearly 7200 or so.
The DL has more units out and more track time so I can understand if someone is skeptical about the newer engine, as they should. At some time all engines are new and have to prove themselves. Having said that, I still like the Area 51 (voted for in poll) better based soley on the way it runs. I have met the owner Milton, at a huckfest event. He is one of those guys that has been contributing to model aviation all his life and he is a grandfather. I did also have great phone and email conversations with Bob at DL, he is also good people in my book. I have the impression that he too is a businessman that came from models - not the other way around.
Here is a vid of the Area 51 runup after 5 tanks of fuel. Sadly I traded that plane away to get my 150cc otherwise I would still be huckin' it.
http://www.youtube.com/watch?v=vLptMPUOj70
Here is a vid from last year of my DL sold to a buddy that has fun with the 88 inch Yak.
http://www.youtube.com/watch?v=2RBCZOPJs5w
Good luck with your choice.
Richard