It is rather subjective and dependent on the intended use or endstate. If you're attempting to conserve weight and rail space, a Vis/IR laser module and separate Vis/IR light such as the M600V, is going to be lighter than an ATPIAL/DBAL or MAWL C1 with a standalone white light, generally by 3-10 ounces depending on aiming module and light.
Apart from the MAWL C1, there are negligible differences between the M600V and most IR illuminators in civilian class modules. If you have access to a FP aiming module, then yes it makes more sense to have a combined IR laser/illuminator module and separate white light or a PEQ-16. However, with a PEQ-16 or other units that have a white light, you then get into the potential risk of selecting the incorrect function because of the 1 switch for multiple functions HI/LO for Vis Laser, IR Laser, IR Illum, Vis Illum, and the combinations for VIS or IR. It's not really an issue, but something to consider.
ETA: The PEQ-16 is quite intuitive, offering VIS: Aim, Light, and Dual; IR: Aim Low, Dual Low, Aim Hi, Dual Hi.