I agree with gurpreetsingh, though perhaps the above comparison should be:
GMATPrep >>
MGMAT > Kaplan
GMATPrep enjoys a comfortable lead in first place; there's simply no substitute. Manhattan's scoring is decent and the questions are challenging, but it cannot match the GMATPrep in terms of accuracy or "feel." Kaplan, from what I understand, is improving, but the tests are still somewhat off.
But do you plan to incorporate all of those tests? That's quite a bit, so be careful with burnout and don't let these tests replace precious time allotted for study.