How big of a plain is it? I love my DLE engines! Gas all the way baby! I mean would you rather spend $30.00 a gal. Or $4.00?
The smallest engine that DLE has is their 20 and that is a 20cc, these guys have been talking about .40ci sized two strokes or .60ci sized 4 strokes... the DLE 20cc is equivalant to about 1.22ci sized 2 stroke engine. DLE and even DA ( even better engines ) are great, but they are in a much larger class of engine than what was being asked about.
I'm pretty much an electric only sort... I like to just plug and go without having to cleanup after I'm done. The downside to electric at this time is flight time, which in this size is probably going to be limited to around 10-15 minutes max... and that is all. An electric motor has more power without any delay when you give it the "gas" than a nitro or gas powered engine. Of course then there is the sound side of this... which, if you wanted, you could add a sound module and speaker to an electric to get but that just adds weight to do it.
To get the right sound on a nitro... you'll want to go with a 4 stroke over a 2 stroke. To go faster, you want the 2 stroke over the 4 stroke. For more power ( torque ) the 4 stroke wins over the 2 stroke. The .40ci 2 stroke equivalant in a 4 stroke is around a .60ci size. Here is some other general info about 2/4 strokes which I got from Tower Hobby's website...
Some differences between 4-stroke and 2-stroke engines;
4-strokes are quieter
4-strokes get better fuel economy
2-strokes generate more rpm (11,000-13,000 RPM with prop while 4-strokes rev to around 9,500 RPM)
4-strokes generate much more torque and will swing a larger prop.
4-strokes have a realistic sound like a real aircraft engine.
Tony mentioned that OS is the best engine out there... I'll say that they are instead the best in their class since there are other brands that can and do surpass them... for a cost. OS motors are known for their reliability and quality and as long as you aren't going with their economy line ( the OS 46LA ), you probably won't find a better motor. I can't say which is the better one between the AX and FX... though I didn't see the FX as available any more as new in a quick search.
I've heard that Thunder Tiger's are good engines but I'd guess they are going to be a little bit under OS in the reliability area but still a quality engine. I've seen these fly/run and they are quick but the guys that have them do have to tune them more than the other guys running OS engines. I've only just heard of Evolution engines but I've never seen anyone with one.
If sound is important to you... go with a 4 stroke... do NOT go by which one is loudest. Loud is a quality that is fun at first but quickly becomes old and tiresome over time.
If you are planing to put this in a warbird or other plane that has a long nose... keep weight of the engine/motor in mind. P-51's and Spitfires are notorious about nosing over on landing... the 2 stroke will actually have an advantage here but you have to sacrifice the sound and smooth running.