Start with the bottleneck, not the category. The right first tool is whatever fixes the thing currently costing you money or sleep — usually time tracking if you bill hours and leak them, a CRM if prospects fall through the cracks, or project management if delivery is chaos. Buy for that, then expand.
Decide consolidate-or-best-of-breed early. An all-in-one like GoHighLevel or HubSpot replaces five subscriptions with one login and one bill, but you trade away the polish of a specialist. Stitching together Pipedrive, ActiveCampaign, Asana and Toggl gives you the best of each, at the cost of integrations to maintain. There is no universally right answer — only the one that matches how your team works.
Price the team, not the plan. Most agency tools charge per seat, so the headline figure is a fraction of the real cost. A $10/user tool across a 12-person team is $120/mo, and that compounds as you grow. Always multiply by your actual headcount before comparing.
Make sure it survives client involvement. Agency software lives or dies on whether you can safely let clients in. Client portals, guest users and white-labelling separate the tools built for agencies from the ones merely sold to them.
Trial before you migrate. Almost everything here has a free plan or trial. Run a single real client through it for a week before you move your whole operation — switching costs are real, and the demo never shows you the friction.