The data question comes first
The most important question is whether you can take your clients’ records with you, in a usable form, without asking permission. Some platforms make exports simple and complete; others restrict what can be taken or provide formats that are hard to use elsewhere. Clarify this before committing any client to a platform.
HelloBooks lets the firm own its data and export it. Whatever vendor you use, run a test export early and check that it includes transactions, contacts, invoices, bills and attachments. An export that looks complete in a summary may be missing detail you only notice during a migration.