How long to rest in between sets?
My answer is very short and I am very biased when it comes to this topic. My answer is- rest as long as it takes you to feel rested!
When I workout I feel that each exercise needs to be very goal specific. You need to be shooting for certain strength goals that you are looking to hit each and every workout.
If you have a strength goal to hit for all of your sets and reps, rest becomes more and more important. You need to save energy to maintain your strength and power.
Rest may come at any time, you may feel ready for your next set after 1 min, or 2 min, or even 3 or 4 min, and thats completely okay! Walk into the gym with a plan and perform when it is time to hit your next set!
Do not be so hard on yourself as to when you should hit your next set. Have a plan that is about the numbers in the gym that you are going to perform when you get there. Rest as needed. Rest when you are recovered and ready to go.