I have a couple of Victrons (older BMV 600 on boat; BMV 700 in van), and also run a Smart Gauge (which Greg mentioned above). I like them both because I like data and like to see just what's happening, but if I only wanted one or the other? Hmmm.... I guess I'd go Smart Gauge if what I really wanted was a really good handle on my SOC (state of charge percent). (presuming not using lithium batteries as it can't do lithium)
The Victron (or any coulomb counter) also gives you great info, but maybe some of it is stuff you only need to know one time or can calculate (e.g. what is the draw of X item). And you have to keep up on adjusting it as your bank ages. It can show you how many amps are still going into the batteries (like say if you want to adjust how long your solar controller is in absorption by manually doing "end amps"). And it's just fun to look at.
But for a good, simple, solid SOC? And if I didn't want to spring for both? Smart Gauge, I think. I poke that 50 times for every 1 time I check the Victron (after the novelty of the first few weeks).
Not that it's a big deal, but SG doesn't use a shunt. Just two small wires (14AWG, IIRC) to each battery post. So if a shunt is intimidating, that's a plus.
I still like both