Welcome to GN's Remmbo,

GME or Uniden mounted units usually outperform hand-helds. Hand-held as an additional unit/s good idea when shopping or sightseeing away from vehicle.

Welcome Remmbo,
Oricom is another reasonable unit, both in fixed & hand held.
GME is made in Australia so you may pay a little more for that brand.

Aerials - the fixed aerial with 6dB gain is most widely bought, 3dB gives you a less directional coverage, but is better in woody areas & 9dB is better in open country but gives only a narrow transmission, reception beam. UHF transmission radio waves mostly travel in a straight line.

Personally I've always used an Icom 400 pro in my vehicle. Yes I'm well aware it's not lawful but I've had it's transmit power tricked up a little..., so I get out a bit more easily and that's very important in the flat country of the central west and north west.
Unlike many other brands the Icom has little or no background snow. And a selection of antenna can be very useful.

I much prefer fixed as opposed to handheld options. Installation is a simple process really but if you don't want to install a UHF, take a look at the GME TX3120SPNP Plug and Play Kit. By the time you purchase a 5W handheld that's easily recharged in-car, you're up for a fair cost. If you want to use a second handheld to assist with reversing, you only need a cheapie 0.5W unit.

Before heading off on our current journey around AU I purchased a hand held 5w TRX brand. It has been invaluable to talk to road trains & wide load trucks etc. it has good battery life along with clear sound. Not expensive and purchased from a camping store.