I prefer full ring, but I would rather be on a good 6-max table than a bad full ring table. If you are a cash game grinder you should ideally be able to play both formats well for better table selection.
For me the main difference is, that there tend to be a bit more "fighting" going on at 6-max with for instance regulars 3-betting you 12% of the time. And since this is not, why I play poker, I often find it better to be on full ring tables, where I have to contend less with that sort of thing, which allow me to better focus on the fish.
Also I find, that 6-max tables are extremely easy to break, mainly because they rarely have more than 1 fish on each table. So often it can be really difficult to keep a table going, and I sometimes feel, like I am in an airport spending way more time getting in and out of tables than actually playing.
This is also because, I dont want to accept the seat directly to the right of the only fish, and unsurpricingly this is often the one available, because other regs dont want it either. This whole table selection process is more extreme at 6-max, and in generel its a bit tiring and part of the reason, why I have largely moved from cash games to tournaments.