I agree, 100% on the Larsen NMO-27. Professional antenna that will outlast your vehicle. I'm using one that's nearly 30 years old.
Avoid mag mounts unless you really don't have an option. They work, but as a long term solution they suck. Lots of drawbacks. The benefits are pretty much convenience, and that's about it.
Best performance is going to come from doing a permanent NMO mount on top of the vehicle where the antenna is in the clear. Center of the roof is ideal as it gives you the best ground plane for the antenna.
Mounting the NMO mount isn't horribly difficult but it does take some skill. You can often get a local radio shop to install one for you for a reasonable cost. They'll can route the coax, cut it to length and properly install the connector. Toss in a 6 pack of beer for the boys in the shop, and you can probably get them to put your antenna on their analyzer and tune it for you. Well worth the money.
As for small form CB's there are some good options. Take a look at the Uniden CMX-560 or CMX-760. These have a small RF deck that you can mount out of the way/under a seat, center console, etc. An RJ-45 cord, like what you'd use for your internet connection, can be used to extend the mic cord. The microphone has all the controls in it as well as a small speaker.
Other option would be the Uniden CMX-660, which you may be able to sneak into the center console.
I'm using the CMX-560 in my truck. It's a bit limited in what it can do, but it's good enough for my use, which is 99.99% listening only, and even then only on long road trips.
With any of these radios, adding an external speaker really improves the audio clarity and volume.
With any CB, the antenna is key. Spending a bunch of money on a CB but skimping on the antenna will give you poor performance.