Lei shen by far.
People keep saying "garrosh is a big dps check", but fact is, the check was only really "brutal" one place - first intermission. Sure, the fight becomes alot easier if you skip the second empowered whirl in P3, but by no means was it a wipe getting it - it was just hard/annoying to deal with it. Same goes for P2.5 - most guilds go for one or two whirls, while you can still get to the third and push him over with no real issues.
On the other hand, Lei Shen's checks were just as brutal during current content, if not worse. Getting P1 done before overloading a pillar had tons of guilds wiping, especially on cutting-edge (and to an extent where alot of guilds used lust in P1). P2 was less difficult in terms of check, but P3 again had a very hard soft enrage - 4-5 thunderstrucks and you were about at the limit, with people getting chipped off one by one by static shocks and spike damage.
On the other hand, as Mione says, getting more gear when you've HIT the "soft" enrages of the fight doesn't make Lei Shen much easier. It does for Garrosh.