....I be using it for patrol, personal defense and swat training. What are your all thoughts on which one would be best?
Check first with your department that what you are planning to purchase is authorized for the use you have in-mind.
If it doesn't meet with this requirement, it's a hard stop, right then and there.
... but heard bad things about small barrels ar15 guns.
Do you mean short-barrel? Or a thinner (i.e. "pencil") barrel?
Neither are absolutely "bad." However, either can be a potential concern, depending on your anticipated use.
Modern 10.5 and 11.5-inch 5.56 AR15s, using appropriate ammunition, offer more than sufficient duty/defensive capabilities. Currently, SMEs favor the slightly longer 11.5 platform, but if you are looking to suppress the weapon and intend for its work to be from within the confines of the vehicle, that extra inch shorter may be worth the potential reliability and additional maintenance compromises to you.
Know that SMEs in CQB such as John "Chappy" Chapman suggest that neither the 14.5 nor 16" variants of the AR15 are untenable for CQB use in CONUS structures. But again, if your team favors suppressor use, having that extra length and weight out at the end of a 14.5 -not to even mention a 16-inch gun- will at the very least prove taxing for you, physically, during longer engagements. Even a "lightweight" gun seems to gain pounds by the second in just a training scenario - and even those with heavier, suppressed SBRs -such as with use of a DD Mk18 or LMT MRP as the base platform- will admit to unwelcome fatigue at the end of longer training days.
Towards the "lightweight" side of the equation, if what you had meant above with "small barrel" reflects instead a question about the "pencil barrel" or other similar lightweight profile barrels (versus the typical "Government Profile"), yes, it's true that the pencil barrels will heat up faster and thus potentially "open up" a bit in terms of absolute accuracy/precision. However, in the real-world, overall accuracy/precision is usually much more an operator-limitation (i.e. how well
you shoot) rather than one that can be traced to the barrel profile, especially at distances of under 300 yards. Furthermore, unless you engage at-cyclic or with massive, repeated mag-dumps, barrel profile typically also isn't an issue (that your department is requesting its members bring their own rifles likely means that it does not have full-auto lowers for you to use, so the former is moot; that a patrol officer is unlikely to be carrying more than one or two spare 20- or 30-round 5.56 AR15 magazine on their usual patrol gear means that the second is unlikely as well).
