Start with the actual offering
Ask which instruments, account modes, order types and reports the broker enables on each platform. Platform software capability does not guarantee that every function is offered on your account.
Automation migration takes work
MT4 and MT5 use different programming environments. Indicators and expert advisers may require porting and testing; the same strategy name does not guarantee equivalent behaviour.
Compare costs on each account
A broker may attach different commissions, symbols or minimum sizes to the two platforms. Test the relevant demo and record platform-specific terms. Neither platform removes market risk or verifies the broker’s authorisation.