Vacuum level is perhaps the most critical consideration.
It affects each of the other factors, as you obviously need a gauge that measures at your working pressure. Typical classifications and ranges include:
Rough vacuum: from above atmosphere to 1 mbar
Medium vacuum: 1 mbar to 10 -3 mbar
High Vacuum: 10 -3 mbar to 10 -9 mbar
Different Gauge technologies are required to achieve different vacuum pressure ranges. Depending on the target vacuum level, a mix of Gauges might be necessary to get measurement across the entire pumping range.
Rough/Medium vacuum gauges — there are many options, including both Direct and Indirect gauges, so knowing the process requirements is vital for choosing the right gauge.
High and ultra-high vacuum gauges — slightly fewer options, with the area dominated by either Hot Cathode or Cold Cathode type gauges, both of which are Indirect gauges.