Soarrich pretty well summed it up.

I own a 3mm that I bought because its case mounted carb and short length best fit a scale application I had. Great running engine and much smoother running overall than my DA or even my excellent Taurus. My 3mm has the hop up kit and I would highly recommend this engine.

I wouldn't hesitate to buy the DL either if it fit my application at the time. But then there are quite a few excellent engines coming out these days. The Area 51 looks interesting as does the MT57 plus about a dozen others. These Chinese engines are really coming of age.

There is no such thing as "the best engine" but there are many good engines. Do your home work and pick one that best fits your application. Sometimes a side carb works or fits best in a particular airplane, sometimes a rear carb works better. Maybe an engine on standoffs works best, sometimes a radial mount works better. Not sure which one would best fit your Eagle. It is great to have choices.