My top initial upgrades were:
1. Defib
2. Grenades
3. Squad pod beacon
4. Advanced med pack
5. Explosives pack
To be honest the personal squad scan drone is useless, I have the armed drone too but the majority of maps it's better to deploy the squad beacon to allow you to retake the map bases easier.
Sentry turret is good, however the more people now with EMP grenades means the less potent these are now.
I really hope they patch it so it remembers your customisations in future.. it's really annoying that it doesn't.