Your not the only one unsure of the differences between the services Whisky Oscar Golf - unfortunately a lot of pilots have never had these services explained properly in the past, so don't feel ignorant . Now some answers :
1. AWIS gives wind speed and direction/ cloud base and approximate coverage/temperature and QNH. The main restriction with AWIS is that the sensor at the unit only has a very limited field of view and sometimes it will state "no cloud" when there is a lot of cloud out of its field of view. No substitute for a pair of eyes giving accurate cloud bases/types and visibility over an ATIS but in most circumstances quite OK.
2. Traffic passed by CAGRO'S is on first contact with all aircraft either at 30nm inbound ( dependant on the size of the CTAF) or when taxying for departure. This is presented in the same format as ATC does in G airspace from IFR to IFR and assessed for relevance using established traffic criteria. The main difference between ATC tower and CA/GRS is that CAGRO'S provide traffic information and NOT separation and only within the confines of the CTAF. They have no radar access .Most other services are the same. As far as Unicom goes, the traffic they can provide is restricted to ETA'S and ETD'S as explained in my previous thread. As this service has never been tested before in a busy CTAF its anyone's guess what advantages , if any, it will have.
3. Cost ? According to CASA documentation CA/GRS is between $50,000 to $100,000 a year and an ATC tower between $500,000 and 1 m a year - NPRM0006AS refers. This is mainly CAGRO'S/Controllers salary after initial set up costs. Unicom has yet to be costed at this time.
The level of safety for CAGRO and ATC is proven and tested. I personally feel the is no substitute for someone professionally trained with a full view of the movement and circuit areas. The safety provided by Unicom is so far untried - but I guess we will find out after the trials.
Hope this helps.