I don't actually do hard intervals all that much anymore, but instead focus on threshold for most of the winter and spring. That gets curttailed in the summer because it's too hot and humid for much of any intensity. But I have the most race success when my threshold is highest, and tabatas and vo2 and similar really don't do much for me. I do like periodic 30s seated high power efforts with 60 sec recoveries workouts for nm work. But suprathreshold work really doesnt seem to give me much gains compared to threshold.
A 45 to 90 min sweetspot interval or 30 to 60 min threshold interval are my go-to now.