Speaking from personal experience, you should avoid round base plugs if you wish to walk around with it in (the base is the part that sits outside of your anus). Round bases tend to get annoying when moving around a lot as they put a lot of pressure on your butt cheeks. This can create a rubbing/pinching sensation, which in my experience can become very unpleasant. Rectangular bases are the most comfortable that I've found as they sit between your butt cheeks much better. There are several options that feature a slight curvature in the center of the base, near the neck. These are very comfortable as they allow your butt cheeks to comfortably adjust around the base.
I have worn plugs for several hours in the past, but they have always been smaller, rectangular based ones. You'll find that you probably will have to settle for a smaller sized plug to meet the comfort needs. Larger plugs need larger bases to act as a secure stopping point. Large bases are obviously not great if you plan to do a lot of moving with it in.
Also keep in mind which material you want to use. I personally like medical-grade silicone. It is easy to clean, does not retain smell, and is pretty common to find. You do have to use water-based lube with it (silicone lube will melt the plug). There are lots of different materials out there, so choose the one that suits your personal needs best. I try to avoid materials that I'm not sure of, or do not detail that they are safe for extended periods (hence why I stick to silicone mostly).
You should also try to find ones with a longer neck if possible (they are hard to find though, so don't worry if you can't). Longer necks put the largest portion of the plug further away form your anus. This puts less pressure on your sphincter, which is better for your body and sphincter muscle.
Keep in mind this is based off of my own personal experiences, and may not be true for everyone. I hope this helps, and good luck in selecting your next plug
