Freenas server and advice on HBA

Currently have two dell r720 servers running esxi with slow local storage. Planning on migrating to shared storage over iscsi. I have looked into buying another refurbished r720 but there seems to be some issues with dell RAID/HBA. Can someone please advise if using the r720 server and just sticking in a properly supported HBA card is the right way to go or should I be looking at something else entirely?