With any forum software you need to consider how much traffic you expect to get, if a forum isn’t going to get too much traffic then any paid-for forum software may not be worth the cost (any initial purchase cost and any licensing fee costs - some it may be a one off payment, some might be monthly, quarterly, half yearly or yearly).
If you think that you may eventually get enough traffic to justify to yourself the costs of a paid-for forum software eventually, then as well as considering what free forum software you’re starting out with, also consider what paid-for software to can migrate to easily at a later date.