Intervals for increasing average speed

I’ve been slowing building up my intervals. I think now do 90 seconds hard followed by 3.5 recovery. I’ve increased my average speed from 16 mph over 16 miles to 17.6 mph over 16 miles.

Should I go up to 2 minute intervals with 3 min covert 3x/week?

Or I was reading about 30 seconds all out alternating with 30 seconds recovery x 10 sets. 5 min recovery, then repay 2 more times

Thoughts?

Why not both?