hey bro, good to see u here heh
hmmm... lets see, let me try put it as simple as i can

RS vs NS, its just matter of your personal preference, while some might argue RS looks sportier, provides sportier riding posture and is slightly faster, its basically just an NS with different coverset and handle. Both are almost identical albeit minor difference in engine and EMS. So, in these 2, its just your preference, for under 10k, both provides great value and more fun than their counterparts that is 30-50% more expensive. Maintenance is generally not too expensive either, engine are both based on KTM 200 series platform and both has ABS options.

As for Dominar and Dominar UG, due to UG emergence, the previous model will definitely suffer from severe price dips. But its also good news for new owners, i think you can see D4 used going for around 7-8k ish.

The Dominar UG is just that much better, DOHC vs SOCH which indirectly leads to additional 5 horsepower, torque is as much fun as you'd expect from a large single cylinder, comes as standard with gear indicator, pretty techy looking dual HUD/speed panel, USD forks(derived from KTM), Nitrox rear shocks, dual channel abs and brakes by Bybre. At 15k brand new, its a steal.
That said, if you're looking for a simple decent daily ride, all above is pretty nice choice, but if you have B full and willing to allocate slightly more budget into D4 maintenance, its also a good choice.