There is no reason you should not be able to cast your spinning set up like you can with a kayak. You can sit, kneel, or stand. Heck, if you want, you can even lie down!
Generally
You can easily cast your fly rod and spinning rod with the SUP. Thus, a SUP is your best bet if you want something that will allow you to release quickly. Still, don't ignore kayaks entirely. It can be challenging to cast a fly rod, but it is possible.
The Storage Of Gear Is An Important Consideration
A subculture of the fishing world that has to be one of the largest has to be gear heads. Gear heads are people who want the newest and best of everything. To catch fish, you need the latest lures, tackle boxes, scents, rods, reels, lines, and everything else under the sun, so how much gear you can carry should be essential.
Storage Options For Kayaks
You'll have many storage options if you don't purchase a kayak explicitly designed for whitewater rafting. You can usually store a tackle box or a small cooler in two areas with elastic straps at sit-ins. The paddler also has a flat spot in front of them to store other items and the areas in front and behind. With the kayak's lip, you won't worry about your things falling off.
Storage Options For SUP
There are straps in the front and back of most SUPs that can hold a cooler or gearbox that you can use for a seat.
You can put a few different things there, from a tackle box to food and other smaller items. With rod holders attached to your cooler, you can bring a few different setups, lures, and flies. Now, aside, this is the perfect vessel for the minimalist fisherman. The ship can hold everything you need, but not much more.
Generally
Kayaks are the best for storing gear, and they can hold just about anything you want, and SUPs are great if you paddle out with only the essentials.
Paddleboards And Kayaks With Motors
Many people are unaware you can strap a motor to these boats designed to be paddled.