Many ball valves are selected for specific applications as engineered items.
Start with engineering standards such as API 6D and ASME B16.34 as the minimum criteria.  This will eliminate the valves at Home Depot.
There are full port and reduced port.  Normally we buy reduced except for low pressure compressor suctions, pigable valves, etc.  The ends are flanged or welded.  Flanges are a minimum for line-class block valves.  Welded are applicable for acid gas such as the high percentage levels of hydrogen sulfide.  Most valves that I buy are NACE MR0175 compliant for sour service - even if the gas is not sour.
Most applications require bi-directional bubble-tight shutoff compliant with API STD 598 and fire safe per API STD 607 or SPEC 6FA, 6FB and 6FC.
Ball valves are available as trunion and floating end.  Someone else can explain this better than me.
Offshore we like Zylan bolts and special coatings to keep the ball valve around for a few years before they rust away.
It is good if the valve is maintainable.  That may require lubricating connections etc.  Some valves have welded bodies that must be removed and sent to the shop instead of serviced in the field.  I forgot to mention top entry valves that may permit service with the body in the line.
Elastomers have to be compatible with the fluid.  Some absorb CO2 then explosively decompress.  Some are eaten by amine, etc.

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