Challenge High Mass Fiber cloth is better against UV, but does have higher stretch than Marblehead - everything is a tradeoff. A few years in SE Asia
will not cause any significant UV issues with any good, low aspect Dacron as long a you cover sails when not in use.
Warp oriented Dacron: Challenge has been working on / improving it for 25 years. I used to run tensile tests on it and the number always come up low. There is a fundamental problem which is getting enough warp yarn density, with low crimp, to make cloth strength appropriate for weight. So it ends up with stretch. This can be improved with resin, but makes it a poor choice for cruising sails. Using it in radial construction does reduce bias stretch (over crosscut sails), but I haven't found that benefit great enough to overcome it's inherent strechiness. So in short, it's fine for smaller, economy radial sails, but otherwise I'd give it a miss.
Lastly, high aspect Dacron - meaning fiber density greatly slanted into fill direction and reduced in warp direction - does make high aspect sails lower stretch BUT has a serious UV problem. The small warp yarns suffer UV in 2 to 4 years (in tropics) - despite the stretch benefit, this cloth is a poor choice for any tropics bound boat unless you count on replacing sails often. And to be clear, most different lines of Dacron, irregardless of who made it, come in high aspect and low aspect. So it's a choice.