I use smoothie/bubble tea straws. I love them. They are easy to cut, brightly colored so a client wouldnt miss them while pulling apart their cake, and cheap! I havent had any problems with them strength wise. The thickness of them makes them quite strong. But for larger cakes (very heavy or very tall) I use the the wilton plastic dowels and plates that lock together since I don’t use center dowels in my cake. To cut the plastic dowels I use a pvc pipe cutter that my dad picked me up from the hardware store. Its small and SO easy to use. All you have to do is put the dowel in the blade where you want it cut and squeeze the handle until it cuts through! Simple clean cut every time right where you want it!
Since I always use them in fondant cakes I like to measure the dowels JUST taller then the cake. To do this I stick the dowel in the cake and mark it with an edible food marker. Then I pull it out and cut it and stand my cut piece with the next dowel, mark it even and then cut that. Continue until all dowels are cut and stick them in the cake. The entire process is really easy and never takes me long. If you cut your plastic dowels too short the plate from the next tier can crush your cake and crack your fondant. I learned that the hard way!