Time to a working pipeline
At this stage the most expensive resource is founder attention, so the single most useful measurement is how long it takes to get from a signup to a pipeline holding real leads with real stages. Some systems reach that point in an afternoon. Others reach it in a month, via a configuration workshop and a partner. Neither is wrong in general, but only one of them is right for a company that needs to be selling this week. Measure it yourself during a trial rather than accepting an estimate.
Reshapeability
Early-stage sales processes change constantly. You will add a qualification step, discover it was wrong, remove it, split a stage in two and rename everything twice. A system that makes those changes trivial is worth more than a system that models your current process beautifully, because your current process has a short life expectancy. Test this directly: add a stage, reorder the stages, add a custom field and put it on the layout, and see how long it takes and whether you needed help.
Conversation capture
Deals move in calls and messages, and anything that does not land on the record did not happen as far as your reporting is concerned. Check how calls are logged, whether recordings are stored and for how long, whether messaging threads attach to the lead automatically, and what a rep has to do manually. Every manual step is a step that will be skipped during a busy week, and skipped steps become gaps in the history that make your pipeline review a guessing exercise.
Commercial flexibility
Startup headcount is volatile in both directions. Ask each vendor what happens if seats go down mid-term, whether there is a minimum commitment, what renewal pricing looks like, and whether unused seats can be released. Published pricing rarely answers those questions, and the answers matter more than the headline figure. A slightly higher monthly cost with clean terms is usually the better deal for a company whose plan will change.
Exit cost
Assume you will move systems within three years, because early companies frequently do. Grade every candidate on how cleanly your data comes back: formats, completeness, whether notes and attachments travel with the records, and how long access persists after cancellation. Run the export during the trial rather than believing a support page. This is the criterion buyers skip most often and regret most reliably.