Get a big rectangular mousepad.

Not really. For RTS gamers, the shape of your mousepad is probably the least important ergonomic variable. What matters is size (large enough to never hit the edge during frantic micro), thickness (wrist support if you rest your palm), and surface friction (speed vs control).

The whole curved vs rectangular thing is mostly aesthetic. Curved edges might help if you’re dragging your forearm across the pad, but in RTS your wrist stays planted and you pivot from the elbow or wrist—you’re not making huge sweeps like an FPS player. A curved front edge can feel slightly nicer if you rest your wrist on the pad’s border, but a cheap rectangular pad with a gel wrist rest does the same job for less.

If you’re optimizing for ergonomics, spend your money on a proper desk height and a good mouse. The shape of the pad is a rounding error.