Double-butted spokes are thinner and narrower in the middle of the spokes but these are thicker at both the upper and lower ends. both double butted and plain gauge spokes do not make wheels and rims stronger and stiffer but the difference is in their weights, as plain gauge spokes are heavier than double-butted spokes so these would play a major role in the lifespan of the wheel and prevent bike rims to lose their tensioning while riding through hard and aggressive terrains. many times it happens to lose bike chain moves side by side and causes stuck in the chain, to avoid these problems both of these types of spokes are well and good for mountain and road biking.
The hardness and durability of spokes also depend on the stretching level of the pokes, the better and best spokes also have better stretchiness and when the wheel absorbs bumps and shocks the spokes cause stretching, plain gauge spokes are better in stretching than double-butted spokes. the main risky point of spokes are their higher and lower points or ends, double-butted spokes are stronger and more durable at both of their ends, so both of these types of spokes are better in their own way, it would be better when buying new spoke always use and check the tensioning of the spokes with the help of tensiometer accessory.
Double-butted and plain gauge spokes are not used individually for both front and rear wheels, so it would be better to install double-butted spokes on the non-drive-side of the wheel and plain gauge spokes on the drive side of the rear wheel, this combination is a better and worthy step, in this case, you are using both of these spokes for your rear wheel setup and your wheel remains hard and impacts for longer use.
Plain gauge spokes are not used for mountain biking and hard terrains, the reason is that these spokes would not allow the wheel to remain true for a longer time, after a few rides you will notice these spokes are loosening from the flange hub hole of the hub and the spoke nipples of the wheelsets, while double butted spokes, all of these drawbacks of these spokes is due to the less stretch level of these spokes as compared to double butted spokes. based on this difference it would be better to build your wheel with a half-half setup on the drive and non-drive side of the rear wheel.
If you have installed double-butted spokes in the front wheel and plain gauge spokes in the rear wheel then this setup is going to cause slight wobbling with the double-butted spoke of the front or rear wheel setup, but plain gauge spoke wheels do not wobble, all of these issues are raised due to the weight difference between both of these spokes.
Hub, Spoke nipples and Rim:
Choosing the quality of spokes also depends on the durability and stiffness of the flange holes and rotating torque of the front and rear hub and also depends on the material and quality of the spoke nipples in which these spokes are threaded within the internals of the hollow space of the centerline of the rim, so all of these things would also matter when choosing and selecting new brands of spokes for your front and rear wheelsets.
Double-butted spokes are lighter in weight compared to plain gauge spokes. due to their lighter weight, it has a lot of benefits over plain gauge spokes, when you are pedaling and climbing uphills or hard and you are riding through harsh trails, then you need a lot of force and power to create rotating torque force within the wheel, and lighter spokes would help you a lot to easily produce rotation within the wheel as compared to plain gauge spokes.
plain gauge spokes are cheaper as compared to double-butted spokes, the reason is that plain gauge spokes are old and traditional discovery and the new modern spokes are manufactured as double-butted spokes, based on this difference these DB spokes are also exp[ensive as compared to PG spokes.
Easy To Remove And Install:
Plain gauge spokes are much easy to install and build a new wheel with them, but double-butted spokes have a complex method of installation and removing a broken DB spoke. and also wheel builders take a lot of time to build new wheelsets with DB spokes as compared to plain gauge spokes.
Weight Of The Rider And Stuff:
Spokes also depend on the weight of the rider and the stuff which are carrying by a rider on the trails, DB and plain gauge spokes would play different roles when weight is put on the rear side f the wheel, double-butted spokes do not cause any negative effect and does not lose tensioning of the wheel and does not depends on the heavier weight of the rider and the stuff while plain gauge spokes would play differently and your wheel will untrue after riding for a few rides, so double butted spokes are much better than plain gauge spokes for long term use.
Double-butted spokes do not make your wheel stiffer as compared to plain gauge spokes, it means double-butted spokes would give more comfort than plain gauge spokes.