I wrote a lengthy article on here a few years past going into detail about vehicle UHF antennas if you can find it.

Any of the CBs on the market will be fine, there is little to no quality difference between well known brands and el-cheapos.

Antenna wise I suggest you purchase a simple 4dB antenna for about $50.

Whilst a theoretical argument can be made for using different gain antennas in different topographies in reality it's impossible to understand what's happening RF signal wise without a full understanding of the transmission lobes produced by your installation. In addition with only 5W (or is it 4W?) of line-of-sight power you're not going to be making cross state contacts. Stay with a 4dB antenna.

Edit:

Found it - antenna gain post

Thanks Mike.  I respect your guidance on this.

My experience suggests there can be a big difference in quality of sound, ease of use & long term reliability between the well known brands, in fact within a particular brand's range too.

It is not uncommon that once respected brands now offer cheap options which are rubbish, but they sell, trading upon past reputation for the brand name.

I fell for this when I purchased a cheap Uniden dash mounted unit. (UH7740NB) for which I paid $239 bundled with an antenna in 2013. It was professionally fitted, but always had intermittent noise interference, but not on all channels. Over the few years I persisted with the damn thing I consulted many folk more knowledgeable than I about such things & tried many solutions, none of which worked. It's operation with the squelch control, a concentric knob on the same shaft as the volume & on/off controls was the epitome of poor design. Finally after very little use (because it was so awful) it's led screen suddenly died making further use of it impossible.

This was a blessing in disguise. We were in the final stages of preparation to depart on travel without time limit, & I bit the bullet & bought a new unit. This time however I sought advice as to what was worth buying & what was not. The new unit was fitted using all the same connections that the old one had used, but now I had a far easier to use, clear as a bell sound quality unit, which now more than 5 years later, having travelled a lot of rough outback roads etc still functions as well as the day it was first fitted.

The recommendation made to me, & which I am happy to repeat to others is the Japanese made Icom brand. Ours is an IC-450 with controls & speaker in the hand piece. It may have been superceded by a new model now? During our travels we have spent a reasonable amount of time on a variety of outback stations & rural properties where both in-car & handheld UHF radios have been in everyday use, & without exception we have found the brand of choice at every one of those locations has been Icom which say a great deal about 'what works well' .

I now believe that the Uniden piece of rubbish I had must have had some sort of internal earthing problem from new. That plus the early demise of it's screen would prevent me from considering any cheapie UHF again regardless of brand. We don't use our Icom daily & it has all sorts of functions we've never used, but there have been many times we've found it extremely useful & once or twice absolutely essential. As for antenna, we still have the whip arial on our bull bar that the man in the shop told us would shake itself to bits crossing the western deserts several years ago & it still works fine. It is the Uniden 6.7db antenna which came bundled with the Uniden UHF radio - which for our touring purposes has given us no reason to change.

EDIT (added)  We also have a pair of hand helds - older GME 5w models., good units, but 40, not 80 channel. It wasn't until we lent them to friends we intended to drive the Cape's Old Coach Road with that we discovered a volume problem bad enough to make them unusable. Our car UHF is 80 channel & the handhelds 40 channel. The handhelds work fine between themselves but between the 40 & 80 channel units one could be heard without problem but the other at full volume was virtually inaudible - certainly not loud enough to be used in car with the engine running. Friend went & bought an 80 channel hand held & all was fine.