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OP. Go Shootas. Here's why:
Ork shootas are one of the most versatile units in the game, currently. The units that trump shootas in combat, are also the same units that trump choppa/sluggas. The bonus to Shootas is that you also gain a 2 shot 18" range gun, and can produce prodigious quantities of firepower whether you're on the move or not. There's also the added bonus of being able to deal with the true heavy-hitting CC units, at range.
Choppa/Sluggas on the other hand gain +1 attack in exchange for having at best a pistol at range. 1 shot at 12" doesn't do much aside from annoy units. Plus there's little incentive to take Big Shootas or Rokkits amongst your choppa/slugga mobs, as their typically going to just be running at your opponent. This leaves choppa/sluggas as a very 2-dimensional unit, unable to deal with anything effectively outside of charging it. That sounds ok, until you also realize that 5th ed brought in the abysmal rule known as 'No Retreat!', and there are many (many) units that out-perform choppa/sluggas in combat.
Generally speaking, Shootas > Choppa/Slugga. They're more versatile, and allow for a wider variety of tactics and usage. A smart Ork player has at least 1 or two mobs of shootas. However you can not only get by without Choppa/Sluggas, but you can completely out-shoot many other 'shooty' armies as well. People stop laughing at BS 2 when you're throwing 120+ dice at them and their precious hammernators are dying to buckets of armor saves.