High intensity vs lower intensity

2 questions
I am currently doing Insanity and doing it most days. I am on day 18 after about 25 days. I've had a few rest days or cross training in between. I did Davina Fit in 15 one day and had sore shoulders the next day whereas I am not really feeling sore after Insanity now. I have a million exercise videos but I am thinking of giving them away because they seem to easy now compared to Insanity but I don't know whether to because of q)2.

Question 1 (about Insanity) - Should I follow Insanity exactly or do you recommend to mix it up with other workouts? Do you skip missed days or push the workout back? I did Plyometric Cardio Circuit instead of Cardio Recovery. Cardio Recovery does nothing but I counted that as one day. Like I said about Davina, I felt sore in different places from doing different stuff.

Question 2 - Is it better to do a very high intensity workout not very well or a lower intensity more consistently? I sometimes just collapse after a round of level 1 drills in Insanity and take breaks or just do knee pushups. Is it better to try and do this or do an easier version but not give up. I still can't do a pushup. I sweat loads (probably the most) in Insanity but take quick breaks through some parts. Or is it better to do an easier workout but do everything without stopping.