Compared to in-camera slo mo...I find none of it truly acceptable.
Twixtor obviously is better.
Premiere is fine for a slight adjust of time. eg 20% ish either way.
DI out of AEFX ...better than Premiere.
Dont do slo mos much in PPro though because generally I will overcrank on a shot even knowing its a bit too slow for task...then speed up in Premiere.