Depends on your setup, I prefer an integrated R-8 arbor on most of my chucks, with a power drawbar it is quick to change chucks/tooling. The downside is the head needs to have more clearance height to remove the arbor. I often use my chuck to hold an end mill, so maybe a bit lazy, but it makes quick work when frequently changing bits, drills etc.. My chucks (both keyless CNC and CNC keyed) all have a TIR of under 0.001", maybe it also is that I am not a big fan of R-8 collets when trying to get endmills in and out with a power drawbar. They are wickedly sharp and even a small twist and they can do damage to your fingers. One reason why when using R-8 collets for end mills I always hold them in a towel when clamping up on it with the power drawbar. I have also had them kick out with the collet and fall on the table. The CNC keyed chuck is very rigid and quick to change cutters/drills. A TTS system is very nice but expensive. Matter of preference.
ER-40 for drills, really do not see the need or hassle, a standard chuck works just fine an is much quicker. Run-out is less of an issue relative to the drill bit. I would use an ER system for end mills, but not for drills. Also something to consider, ER collets come in increments, their range is more limited then what they claim, toward the limits of their range they become quite inaccurate, in particular using a metric set for imperial size tooling. They are also slow and somewhat awkward to be continually switching out collets for different size drills.