CO as a rule, has clean planes, good staff and decent food. If you're in J, be aware the seats aren't flat. The check in at terminal C is usually fairly painless, but I do recommend on line check in if you can get it, it will save you a good piece of time at the airport. The president club is quite nice, free wi fi, free drinks and snacks, and the 777 usually has AVOD.
The security in C has some line length, as it serves all the CO
Sometimes it is faster to check in at the B terminal (CO Express) and then do security there, and take the airside terminal transfer to C.
Also, if you're not going to be in the lounge, the C terminal has some decent places to eat, get a drink, etc.
If you're a smoker, be aware there is no smoking room in the terminal.