LOWEST. STANDARD. ROOM.
If the MSC or client wanted you to book a suite, they would have instructed you to book a suite.
They usually want you to evaluate the check-in process; does the reception associate offer you a suite? No? Then you write about it. Yes? Lucky you! Then you write about it. If you want to be "ballsy", then you can inquire about an upgrade when checking-in.
By booking a room/suite that is more expensive than what you were instructed to book, takes that room/suite out of the client's inventory, negating the possibility of them receiving revenue for that said room/suite versus them reversing charges or reimbursing you for the lowest standard room. Additionally, they may want you to evaluate the lowest standard room and not a suite.
Booking a room/suite different than what was instructed may be cause for you not to be reimbursed and your report/shop to be rejected. YMMV.