How long is your cable run - and what antennas are you using?
For bag work where I am using dipoles and the cable length is fairly short I personally like something like an RG-174 (or something similar) and terminate on one side to a BNC and the other to an SMA. For longer runs you may want a beefier coax which would be hard to terminate to a SMA so in which case you would need to terminate to BNC and adapt it to SMA.
As a general rule the shorter the cable run and the less adapters = less loss.
Also make sure you use 50 ohm coax and connectors.