Flexible and Autonomous scale in different ways: Flexible lets you resize server resources, while Autonomous is designed to add capacity automatically beyond its baseline.
Vertical scaling helps sustained growth
Cloudways Flexible can increase CPU, RAM and storage within provider constraints. That is appropriate when the baseline workload has grown and needs more standing capacity.
Autoscaling targets variable demand
Autonomous is built for WordPress workloads where concurrent demand can spike beyond a fixed baseline. That can reduce the need to predict the exact peak server size in advance.
Scaling does not fix bad application behavior
A slow query, runaway plugin or uncached endpoint can consume additional resources at any size. Profile the bottleneck before treating capacity as the only solution.
Decision takeaway
Choose Flexible when you want to control standing capacity; choose Autonomous when automatic response to variable WordPress demand is central to the requirement.