I own both and I think you should just buy both too, but ultimately, I think you will prefer the SL Jr Lux for its everyday ease of use.
Although I like my Gerber LX 3.0, it's a little too heavy to carry around in the front pockets of my overalls and the extra weight causes it to be slightly annoying in the side-leg tool pocket as well (though the Gerber's extra length makes it easier to "draw" from that location). The Gerber is built like a tank, but I feel the extra weight is overkill.
And as was said by others, the Gerber's twist-on tail cap slows me down and requires that I use two hands to turn it on (though by backing off the tail cap by 1/10th-a-turn, you can use the Gerber in momentary-on mode). I much prefer the Jr's one-handed clickie (although I think mine is a little too hard to depress).
The SL will just suddenly go out on you when the batteries get weak, so I feel the need to carry extra AAs in case that happens. The Gerber just gets slowly dimmer, so you know when it's getting time to carry spare batteries or when to just replace them.
Another thing, I use my lights at work and the silver-colored Gerber is now covered with embedded dirt/oil stains and has lost some of its original beauty - if that matters to you (I could try washing it I suppose). Because the SL is black, it hides the dirt and still looks fairly new (but with a few nicks).
One of my SL Jr Lux's has developed spider web cracks all over the reflector surface. It doesn't appear to have adversely effected the beam so far, but I may make a warranty claim in the future. The Gerber has a little battery rattle which harms its sturdy feel (you could easily line the battery tube with something to get rid of it though). If the SL Jr. has some battery rattle, you can just screw-down the click switch a little tighter to get rid of it.
The Gerber is brighter, and once in a while that comes in handy, but when I grab a light on the go, I always grab the SL.
-gvmelbrty
