I know the extra power seems attractive but really ...are you going to drag race other 300s or a KLR650 ?
The high revving alternatives might be fun if you are willing to keep them well up in the powerband where the extra low end torque of the CB300 makes it an easy bike to ride and it certainly keeps up with traffic ( tho maybe not Toronto fast lane in rush hour ).
The ABS will let you push the limits of braking without getting you in trouble even in the wet plus will add to the resale value.
I put 300 km on my CB300F today on everything from 100kph sweeper highways, to insane twists on the Gillies ( 210 curves in 19km ), rough pavement then a tiny bit of dirt two track. Appreciated having the ABS even tho did not kick in at all.....I have 57 years riding and ABS only in last 15 years so muscle memory for threshold braking is extensive ....rarely did ABS kick in but both times was a save the day situation.
Yeah the 300 it takes a bit of extra shifting but it is light and agile and much fun.
No, ABS is not a deal breaker but ......the 300 singles have their own appeal ( I rode a BMW310 for an afternoon ) and ABS soon enough will be mandated ( might even save you some insurance now ).
my 2cents.