Standalones really give you the flexibility to do whatever want. You have you ask yourself what you want out of the ECU? For example I’ll use myself.. all I cared for was going MAP, flex fuel, and modern engine protections that aren’t available in the oem ecu. So for me the haltech platinum pro v2.0 was perfect for that. It had the perfect amount of inputs/outputs available to run all of that, including 2 haltech boost solenoids, and an IAT.
A more advanced and more superior version is the Haltech Elite which offers even more. Really depends on what you want out of the car. Also make sure you choose an ecu your tuner likes to use!!!