I think it really depends on what you want to improve. When doing 30 day shred for the first time, I did think each level was harder than the last. Now I can go back to it for an "easy" workout and depending on which one you do, will depend on whether you want more cardio or more strength. Level 1 gives you a taste of both, level 2 has more intense cardio and level 3 had more strength resistance exercises.
So in saying that, if you want to increase your strength, start with increasing your weights. If you want to get your heart rate soaring again, go to level 2. But in saying that, your body may need a change if you have been doing level 1 for a while. Your muscles might have got used to those movements so increasing the weight wont help, whereas changing the routine will force them to adapt and strengthen again.
If you want a real challenge, try increasing your weight even by 0.5kg and going to level 2. Most people tend not to increase their weights when they should, so don't be afraid to up it if you are not seeing any improvement. To test if you need to increase, pick an exercise and if you can do more than 12 reps of a single motion and aren't feeling it that much, time to increase your weights.
| current weight: 139.0