Kam, if you're familiar with classic (that is to say, 1960s-1980s) Legion, then you shouldn't have much trouble jumping on with the two #1s. There'll be a couple characters you won't recognize, but they don't play key roles and you'll doubtless have time to get to know them. Both series start new storylines with #1 and referring back to preboot has been minimal (though present, especially in the core book). I'm enjoying both books, but if I was gonna pick just one, I'd pick the core book written by Levitz. I just got my hands on it today and there were some nice moments with Cham, Ultra Boy, Mon-El/Brainy and some others.

Samy wants to see the following collected editions:
X-MEN: CLAREMONT/JRJR OMNIBUS, X-FORCE OMNIBUS VOL. 2, 
NEW MUTANTS OMNIBUS VOLS. 1-2, GENERATION X OMNIBUS
PUNISHER (1987) #1-18 OHC,
PUNISHER WAR JOURNAL (1988) #1-24 OHC,
X-MEN: REVOLUTION OHC
X-TREME X-MEN VOLS. 1-2 OMNIBUS, WOLVERINE: HAMA/SILVESTRI OMNIBUS,
LEGION ARCHIVES VOL. 14, KNIGHTFALL OMNIBUS
LEGION OF SUPER-HEROES: EYE FOR AN EYE DELUXE HC