I'm not sure now whether the technology has improved. But years ago, "electric brad nailers" were oftentimes called "electric brad starters" for their (lack of) power. You'd still need a hammer to finish the job.
The first brad nailer I bought was electric and often left the brads above the surface. Then I got an air powered brad gun that shoots 2-inch brads into hardwood just fine.
My friend got a cordless brad nailer for Christmas that isn't bad but still leaves them stopped above the surface more than an air powered version does.
On a whim I bought a pin nailer and have found it handy for furniture making. Which brings us to air. Any sized compressor will run all the possible nailing devices. If you go air an easily portable, quiet, compressor is desirable.
My little one lunger weighs less than fifteen pounds and will drive brads flush without problems. Not the greatest air capacity, but for small jobs not a major concern. Go with air.
From the responses here and reading reviews on line air makes sense
Now...time to buy
This is for occasional personal use. I've settled 18ga/2". Maybe nail/staple model
Desalt reconditioned tools have been a good value in the past. I found. Wen at HD for under $30 with nails. Wen has struck me as equal to Harbor Freight. For $50 I find a DW. Is there a compelling difference in a more expensive nailer?
Almost all models drive a 2" nail through oak. The most significant disadvantages seem to be weight(between 5 and 8 pounds, size and cost not counting compressor.