It’s vital to develop learning and capacity in both the Quantitative and Verbal areas simultaneously; in that path, there’s consistent “maintenance” of your aptitudes. You don’t as a matter of Course need to think about both Quantitative and Verbal consistently, however intermixing the subjects all the time would likely advantage you over the long run.
Most people find the quantitative section to be very difficult, whereas few people find the verbal section to be difficult. Before appearing the GMAT, when you go for the mock test you will know about your strength and weakness.
While taking GMAT you should start with the section in which you are really comfortable. If you think you are really comfortable in quantitative section then you should start with quantitative otherwise with the verbal section.