Depending on your experience... It's up for grabs... Most people who ride trails on a 2-stroke started out with one. The 4-strokes are a lot more forgiving to rider error especially on adverse and technical terrain. I would say pass on the 125 unless its a screaming deal or the one you're riding is too small. 2-strokes also require some different maintenance approaches. Cheaper in some ways yes, but require you to stay on top of a few things in order to run right. If you decide to go with it there are a few things to help it trail better. Like a flywheel weight, gearing change, suspension upgrade. The first I would do is Suspension.
It'll be different, but if you learn to stay a little higher in the RPM range or lower the gear ratio on your bike, you should be just fine
in general a 4 stroke will be more amenable but I have to say a Yamaha trail 125 stroker will also mange well, riding style adapted to suit. Research the test reports, read between the lines, but from the way you write, a stink wheel isn't for U. It is generally easier to run a low compression 4 cycle than a stinkwheel with lower gear ratios, but that's up to U really. Read all the tests, the blogs etc, form an image......