I'm with Epicfail here. A 23GA gauge micro pinner might be the right tool for the specific project you're describing. But if you only plan to own one gun, I'd make it an 18GA brad nailer. For furniture and glue-ups to light trim work it will probably be your most versatile option. Oftentimes the holes are small and discrete enough you may not even need to putty.
Cordless brad nailers have become hugely popular lately. DeWalt, Paslode, Milwaukee, Craftsman and Ryobi all make one. They're perfect if the project only calls for a few nails and you don't feel like setting up a compressor just to get a couple shots off. As someone who regularly uses both battery and air powered guns, I'd strongly suggest going pneumatic if you anticipate a fair amount of nailing in your future. I own a cordless DeWalt brad nailer and a Bosch 16GA finish gun and while they're both quality brand-name tools, the technology isn't quite there yet. Heavy and underpowered. Paslode's is substantially lighter, but I know several carpenters who aren't crazy about those either as they require costly fuel cartridges in addition to batteries.
As far as trim work goes, I often use a brad nailer for more delicate decorative casing, shoe, and wainscoting panels or other pieces where I'm also using construction adhesive. My go-to though is without a doubt a 15GA finish gun. For larger moldings, crown, jambs, etc, an 18GA just doesn't have the holding power (other than maybe shooting 2" fasteners into wall studs). However, I'm assuming you're not a trim carpenter, so your uses for a 15GA are probably quite limited. Just wanted to put that out there because IMO, no carpenter's tool box is complete without one...and if you plan on doing any home renovation work down the line, it would be an essential addition to your collection. For your current applications, I think a brad nailer would be the way to go. (Being light and easy to handle, they're also useful for temporarily holding pieces roughly in place as they can be easily "kicked" into exact position before permanently fastening by hand or with a framing nailer).
Hitachi makes great, very reasonably priced guns. Blue Sky Tools is a good online vendor of refurbished Hitachi tools (and no, I don't have any affiliation). The 15GA finish nailer I got from them cost about $100 and didn't have a scratch on it. Came with the original manual and a brand new case. Hitachi's 23 and 18 gauge nailers are solid as well. My boss and a carpenter I work with are both Senco guys. Senco's Finish Pro brad nailer is a good gun, and we also have an ancient 15GA that's heavy as a bag of rocks but has been going strong for 20+ years and still works like a champ. So I'd also consider Senco. A cabinet guy I know swears by Grex, but reviews are mixed, and they're pretty darn expensive too. Though once the gold standard in pneumatics, Bostich has really gone downhill IMO. Personally I'd look elsewhere, but supposedly their latest high-end models are quite good; I haven't tried them though, so you'll want to do your own research. Tons of great options out there these days!
Id go for the brad nailer. A short brad should hold the the stops in just fine, and in my opinion youll get a lot more general use from an 18 gauge brad nailer than you would a 23 gauge pinner. Not saying the pinners a bad one to have by any means, for something like installing trim on a cabinet it would be the go to, but a brad nailer has a lot more flexibility