We cannot offer direct suggestions for specific AVL vendors, but I would advise you and your customer to review the options that are out there and ensure they will be able to work directly with GeoEvent. If possible, I would obtain a demonstration account with the AVL provider or get a (hopefully free) trial demonstration that would allow you to test it directly with your GeoEvent Server. Another option is to review the GeoEvent Gallery for connectors that have been developed for other vendors.
When evaluating an AVL provider's API, you should look for some key features:
1. Data is pushed/pulled via one of the OOTB Transports provided by GeoEvent (HTTP and TCP are probably the most popular).
2. Data is provided in a format that is OOTB for GeoEvent (JSON, XML, GeoJSON, CSV).
3. The data can be obtained directly and without chaning parameters on the input. For example, there is no changing time range that needs to be specified on each request, or an access token that expires every 24 hours.
4. The data schema is not overly complex. Some providers require several different inputs to bring in the data in peices (vehicle info, vehicle location, vehicle status, faults, exceptions, I/O status, etc.). This can be done, but each piece of the data will require a separate input and the data will need to be joined in a relational database. Also look out for data schemas that are highly grouped or nested, as these can be hard to flatten in GeoEvent.
5. The data schema will provide your customer with everything they need. If they intend to track snow plows, does it provide all the extra I/O status (plow up/down, temperatures, feed rates, etc.).