we have a pair of Tower iSUPs and they're great. I don't recall which model, but it's a wider, rounder board. I'm by no means a pro boarder, so I really apreciate the stability and grippy surface. I'm sure there are faster, more agile boards out there, but for a beginner like myself it's perfect.
I'm a SUP instructor and have tried several ISUPs. I'm a fan of Starboard myself for their quality and variety of different shapes available. Red Paddle Co is also a nice brand. Cheaper brands tend to be "rafty" and flex a bit. I higher end board with a high PSI will be nice and stiff. If you can get an electric pump for it as well, that is ideal. Save you the trouble of manually inflating in the heat! Plus they usually are able of going in reverse for when you are done and can suck the air out of the board super quick.
What I DON’T recommend:
I bought one of the cheaper and smaller inflatable SUPs. It becomes rigid enough, but it is not stable enough even in very calm water—forget light waves like at the beach.
Make sure you get something that matches your experience level and the location you will use it.