How to choose a weekend warrior's finishing nail gun?
I don't know Brad
There are no &quot;brad nailers&quot; in my lexicon as a former pro and perpetual home improver*. There are only finish/trim nailers that accept either 18ga. or 16ga. nails. Which you need depends on the job.

Most 18ga. guns only shoot up to 2&quot; nails. Some only do 1-1/2&quot;. That's inadequate for things like heavy base trim and door jambs, let alone almost anything outdoors.
16 ga. guns are larger and heavier and leave a larger hole. They can also split delicate moldings more easily. They're more versatile, though, since they offer more holding power. Keep in mind that the surface area of a 16ga. nail is dramatically greater than that of an 18ga. nail. That means a lot more grab. It's not just about length.

To Hose or Not To Hose
The benefits of pneumatic air nailers:

Relatively inexpensive to purchase and operate (assuming you already own a compressor)
Endless fuel supply
Dependable power
Speed (compared to gas-powered nailers--I've never used electrics)
Lighter weight for easier operation and less fatigue

The benefits of cordless (gas or electric) nailers:

More portable
Quicker jobsite setup

Features? We don't need no stinking features.
In air nailers I look for ease of use and longevity. Simpler is better, as they tend to get banged around and weight is a concern. Good ergonomics are also important. There are many types of safety triggers, so find one you can live with. A well-designed nose is also helpful in positioning shots precisely. A big looped wire plunger can make that challenging. A poorly-designed nose can scar your woodwork.
OK, I guess those are features.

Light weight
Good ergonomics
A precise nose with a soft plunger
Simple design

Getting there from here
I might ask myself these questions when shopping:

What jobs will I be required to complete on a regular basis with my nailer?
What jobs would be nice to do with my nailer?
What are my portability and ergonomic requirements or preferences?
What's my budget?

It's a fairly subjective thing. There's no one recipe for success. Buy or rent, try, trade if necessary. Good luck.
* The term is just too nebulous to be useful for describing pneumatic nails. In fact, I think of brads as short, fat nails for making shoes and other olde fashioned crafts, closer to the diameter of a 16ga. nail. The term is centuries old and has been casually and inconsistently applied to modern nails.