With hard drives, it'll make no difference at all. If you want to connect a bunch of SSD's and run them in RAID then that could make a difference, but frankly it doesn't much matter.

However, the 9300-8i you linked (SAS3008 is the controller chipset, the 9300-8i part is the specific product overall) uses SFF-8643 cables like this whereas the 9211-8i uses SFF-8087 cables like this. So you do need to ensure you get the correct cables for a specific board - a handy part of getting one that comes with cables.

If the price was the same, I'd get the SAS3008 based board, as it's just "better", but it doesn't really matter and in an UnRAID system isn't going to affect performance. If I were buying one myself right now, I'd just get (another) 9211-8i board because they're cheaper and will work fine for my purposes for many years to come.