Is the 2-ohm or 4-ohm version better

 

depends on the amp, if you want to run 4 ohm, get the dual 2 ohm and if you want to run 2 ohm get the dual 4 ohm

 

http://www.rockfordfosgate.com/rftech/woofer_wizard.asp

 

Also depends on how many L7's you plan on using . But niether one is better than the other . Different Ohm ratings give you the flexibilty of wiring multible drivers(usually 1-4) while still maintaining the amplifiers load(usually1-2 Ohm) rating .