The following blog post describes and recommends the key features an engineer should consider when choosing a Reed Relay.
Signal Voltage, Current and Power Specification
All reed relays have specified voltage and current ratings that need to be kept within if the reed relay is to have a long service life. It important to be clear if the application envisages hot switch or cold switching, it can have a substantial impact on the cost and size of relay used. If hot switching is likely to occur note the power rating of the reed relay, the fact a particular relay may be capable of 100V and 1A does not mean it can hot switch a signal with these extremes. At 100V a 10W reed relay will only switch 100mA reliably.
If hot switching is not expected then the user can rely on the carry current rating and the rated withstand voltage across the contacts.
SMD or Thru Hole Mounting
For applications where relays may have to be serviced Pickering Electronics recommend thru hole components are used. Outside of this the choice is driven by user manufacturing preferences and component choices such as footprint area, relay ratings and relay height.