LAR+EBR USED TO BE the best loadout. LAR lets you stun scrakes and bodyshot little things, EBR lets you kill FPs and bigger things. It used to be the only loadout to let you solo 6man HoE (realistically).
However, with the addition of the M99, the Xbow's firing speed doubled, meaning the Xbow and M99 are OP, and the LAR+EBR is balanced, so it's no longer as competative.
LAR+EBR is what I generally consider to be the expert's loadout.
Mk23+Xbow is the general loadout most people (including myself) go for thesedays.
Also, since the 9mm is supercharged for sharpshooters, the Mk23 is nice, but not necessary. I'll quite often just use a 9mm and Xbow, even on hardest difficulties.
This gives you 4 blocks free for katana/Medigun/M79 (that one's dumb but funny).
Especially for kiting, Katana/Xbow is hard to beat.