It would help your decision-making process greatly if you could try the bike before buying it. And you should think about what's more important to you--compactness vs. ride quality, along with other factors. For example, in my experience Dahons have a nice compact fold but my Speed P8 is a more fiddly and unforgiving to fold than I'd like. If my pedals are in the wrong position, I have to start over, the magnets can be a little funky to join up, you have to move the cables out of the way, etc. I found the Downtubes I owned had much quicker folds, although the Downtube 8H made a clumsy and awkward package. My Swift folds quickly and far exceeds the Downtubes and Dahons in ride quality/speed, but it's not a compact fold. Etc.

If you're in New York City, we have bfold and NYCE Wheels, which specialize in folders, and many bike shops carry at least a few Dahons.

Since you're looking to take the bike in an airline legal suitcase, you'll need one with 20" wheels or smaller to make it fit.