Splines would be the best way to go. The better shops take your crank, and machine in a slot that is half into the crankpin, and half into the flywheel and then press in a pin to help hold things tight....then weld a small bead, and then finally true the whole arrangement.
I trained as an engineer at Roll-Royce Derby and can hear their derision from where I sit! Welding a crank is not an engineering solution and there are enough cranks out there to prove that, which do not involve welding, except perhaps for the most extreme forms of racing. Nor are splines necessary, with the correct materials and precision. If welding and splines are being done they are as patch repairs and I for one would have nothing to do with that!