Re: 25 horse merc
I have a 1997 Mariner 20hp (same as merc) 2-stroke, it has the same block as the 25 just smaller carburetor and other parts, and it still runs like new.
It gets used almost everyday, and still runs really strong. Really good on gas too.
Always starts on the first pull, after winter storage I put it on the boat and it fired on the first pull!
It hasnt needed any work or repairs done to it and I've owned it since new.
The 4-strokes are quiet, fuel efficient, but have alot more moving parts that could break.
2-strokes are lighter, have more power, and I like the sound of 2-strokes as well. We go waterskiing with my 20, pulls up my brother waterskiing and wakeboarding, he is 195 pounds! havent tried anyone heavier but it probably could handle a bit more.
your choice mostly depends on what you plan on using the motors for. On a pontoon a fourstroke would be better because they are quiet, good on gas and can idle smoothly for a long time. 2-stroke might get a little smokey when idling on a long cruise.
sorry for rambling on, hope this helps!