There is no best PO system in general, and there is usually an obvious one for a particular organisation once three facts are known. Comparing features first produces long evaluations and mediocre fits, because the features are broadly the same across the range while the range itself spans a factor of ten in cost and implementation effort.
The three facts
How many orders you raise a month, how many people raise them, and how often a delivery arrives incomplete. Low on all three and your accounting package's module is probably enough. High on the second and third and line-level receipt tracking becomes essential. High on all three with a dedicated buyer and a suite starts to earn its cost.
Why partial deliveries decide it
They are what document-level tracking cannot represent. If deliveries almost always arrive complete on one date, an order is a single event and simple tools cope well. If they arrive in pieces over weeks, the order is a running account, and that is exactly where cheaper tools stop being adequate and start generating manual work.
What to insist on at any size
Automatic unique numbering that never reuses, approval before the order is issued, receipts recorded by whoever takes the delivery, revisions kept with their dates, and an export you can read without the vendor. All five are cheap in any product and expensive or impossible to add later.
And what to ignore until you need it
Sourcing, tendering, contract repositories, catalogues and spend analytics. These matter where somebody's job is buying and are configuration burdens everywhere else. Buying breadth you will not maintain is the commonest reason these systems end up abandoned within a year.
Questions people ask about best po system
Should we shortlist by industry?
Rarely. Industry-specific products matter where the buying itself is unusual, such as construction retentions. Otherwise sizing matters more than sector.
Can we move up later?
Yes, and it is easier than moving down. Clean data and a readable export are what make any future move inexpensive.
How do we test receipting quickly?
Order ten, receive four, invoice four, and check that six show outstanding on that line. Five minutes and it settles the question.
What should we avoid buying?
Breadth you will not maintain. Sourcing modules, catalogues and contract repositories all need configuring and keeping current, and an unmaintained module is worse than an absent one because people trust what it shows them.