ROF makes a huge difference, to be honest. That's why the ACW is so good, because of TTK.
I find TTK a useless metric as it assumes all of your rounds are hitting the target. Low weapon TTK's typically mean high ROF which in turn get high spread values to balance out. At short ranges ACW is sweet, at medium to long it's bad. In short, it depends on your playstyle as well as do you typically burst/mag dump/etc.
I'm at the opposite end as I like low ROF/high damage -- a la SCAR-H/G3A3. Still not happy they moved the SCAR-H to the assault class and the G3 isn't in the game -- hopefully it shows up in an expansion. I'm using the AK-5C as a substitute for the time being when rolling engy and it's not too bad.