I don't know the G-2, but REL and JL are usually about as diametrically opposed as designs can be. A quick look at test results reveals that the RELs are woofers with extended bass and the JLs are true subwoofers designed for clean output in the bottom octave.
For example:
http://www.hometheatershack.com/forums/subwoofer-tests-archived/6015-index-subwoofer-tests-manufacturer-model.html
Caveat: This type of result may not be applicable to more recent REL designs.
The good news is that you can pick your poison here. I'll take the JL every time, but many prefer REL.
Good Luck
Marty
For example:
http://www.hometheatershack.com/forums/subwoofer-tests-archived/6015-index-subwoofer-tests-manufacturer-model.html
Caveat: This type of result may not be applicable to more recent REL designs.
The good news is that you can pick your poison here. I'll take the JL every time, but many prefer REL.
Good Luck
Marty