I am currently in the market to purchase either a collector to use with collector for ArcGIS or a receiver to use with the app on a ipad, android, etc.
What are my best options?
Please view this resource for compatibility of external GPS receivers with the Collector for ArcGIS App:
GPS receiver support—Collector for ArcGIS | ArcGIS
Post if you have a specific question about a particular receiver not on the list.
Depends on the required accuracy for your project. Eos Positioning offers various high accuracy gnss gnss receivers (from submeter to centimeter rtk) that are all Apple certified and fully compatible cross-platform with Collector (iOS, Android, Windows). Visit www-eos-gnss.com for more info.