I think that's actually 3 questions.
The answer to all of them depends on the transmission and tire size. With the 33s and manual transmission you have listed in your profile, 3.73s would deliver better gas mileage and better power over the 3.07s; however, neither are optimal. I had 3.73s on 30s, then 33s, with a manual for years. I got 20 mpg on the highway once with the 30s, a hardtop and a violent hangover (driving slowly). That dropped to around 14 or 15 with the 33s. I regeared recently to 4.56 and hope for better gas mileage because even though the RPM will be higher, the engine will actually not work as hard to maintain speed.
Numerically higher gear sets are theoretically weaker, but ring and pinion strength is generally not a concern with these smaller axles (vs. one-tons, etc.) for the various gearsets. You can only gear so deep with these (4.88 limit on the D30 and D35; 5.13 on the D44) The weak points are elsewhere.
YMMV, as they say.
Edit, question: Is that yellow Jeep in your profile yours?