[Cherryville Chuck]

A spiral will do a smoother job but they are twice the money of a straight bit and there are 3 types of spirals. One is an upcut design. It will leave a smoother edge on the bottom side of what you are routing. Next is a downcut design which leaves the top edge smoother. Third is a compression bit with the bottom spiraling up and the top spiraling down. It's the most expensive. https://www.whitesiderouterbits.com/collections/flush-trim-spiral-bits

 

[Cherryville Chuck]

If you plan on using this type bit a lot I would get it in 1/2” shank and replaceable carbide cutting edges ( an RC model). It’s a fair bit more money up front but will save you money in the long run.