Start with your batteries, not the nailer. Every gun on this list is good enough to hang casing all day, so the platform you already own settles most arguments before they start. A finish nailer is a sometimes-tool for most people, and buying into a second battery system for one is how you end up with four chargers and a drawer full of orphans. Remember the walls between platforms: Milwaukee M12 and M18 don't mix, Ryobi 18V ONE+ and 40V don't mix, Makita 18V LXT won't fit 40V XGT, and while a DeWalt FLEXVOLT pack runs 20V MAX tools just fine, a 20V MAX battery will never power a 60V tool.
The picks below are based on manufacturer specifications, magazine style, and battery compatibility.
If trim is your trade
The Milwaukee 2841-20 M18 FUEL is an angled option for frequent trim work. Its nitrogen air spring drives 16-gauge nails from a 110-nail magazine. Milwaukee rates it at up to 800 nails per charge with an M18 CP2.0 pack. The angled magazine can make it easier to position the tool in tight spaces.
The other pro pick is the Metabo HPT NT1865DMST, a 16-gauge straight-magazine gun on the MultiVolt platform. Metabo HPT lists a lifetime tool warranty, so confirm the current terms. Check local service and accessory availability before you commit.
If you remodel and the nailer is one tool of forty
The DeWalt DCN660B is a tool-only option for remodelers who already own 20V MAX batteries. It takes 1-1/4 to 2-1/2 inch angled nails. DeWalt rates the DCN660 at up to 800 nails per charge with the 2.0Ah pack specified in its runtime test. If you need a battery and charger, look for the DCN660D1 kit.
Punch-list workers should also look hard at the Makita XNB02Z. Its party trick is runtime, up to 1,000 nails on an LXT 5.0Ah battery, matching the Ryobi's top rating. The price you pay is mass: Makita lists 7.5 to 8.4 pounds with that 5.0Ah pack. On a bench or baseboard it doesn't matter. Overhead, it does.
If you're a homeowner with a Ryobi charger
Buy the Ryobi P326 AirStrike and don't overthink it. It sinks 16-gauge nails from 3/4 to 2-1/2 inches, holds 105 in the magazine, runs up to 1,000 shots per charge, and shares batteries with the drill, the fan, and whatever else is in your garage. It won't keep pace with the pro guns on speed, and the mostly plastic build reflects the price. For window casing on a Saturday and quarter-round next spring, none of that matters.
Straight vs. angled magazines
Angled magazines can be easier to position in corners and tight framing. Straight and angled nail strips are different. Check the gauge, length and collation angle in the manual, then see what your local store stocks.
For daily trim work on M18, start with the Milwaukee 2841-20. If you already own 20V MAX batteries, the DeWalt DCN660B gives you a tool-only option.
Related guides: framing nailers and a cordless nailer that won't fire, plus fixing an air compressor that won't build pressure if you'd rather stay with pneumatic.