This isn't about "the strongest" gear. It's more about having the right gear for your set up...
Look at it like this. Pretend you're riding a traditional 10-speed bike. The 5 gears at the rear of the bike are the equivalent to your Jeep's transmission. The 2 chain-ring gears at the front of the bike are like your Jeep's axle-ratio. If your bike had smaller tires on it, you'd want the chain to be on the LARGER gear up front or you'd have to pedal like MAD to keep up any kind of speed. But if we swapped your bike tires to a REALLY tall set, you'd want to put the chain on the SMALLER gear up front or it would be too difficult to pedal.
Neither gear is "stronger", but just more "right" for your specific set up. By your profile, I see that you have 32" tires, so whatever stock gears you have are probably fine, but if you decide to go to a bigger tire, you may need to pay-up for a gear swap.
Hope this description makes sense...
I intend to live forever. So far, so good.
'99 Wrangler Sport: 2.5" Old Man Emo lift and shocks, adjustable trackbars, Quick-Disko sway links, rollin on 31" BFG A/Ts