Total wpg cause fluctuating temperature due to rapid heat up, be it via 1, 2 or 10 heaters. But a pair of 100w would be better than 1 200w especially if controlled from a common stat, independent stats would lead to a single heater carrying 90% of the duty due to the impossibility of setting two stats at an identical temperature, not to mention their different positions in the tank, different hysteresis curves, temperature float of the stat setting over time and not forgetting Sod's law. Bit saying bad idea, just not as perfect as it could be.
A pair of heaters in parallel set to say 27 degrees. And a series connected stat at 26.5 switching both would be better, the common stat would cleanly control both as the built in stats would never reach 27 to shut off unless the control stat fails, at this point the bck up stats will click out at 27 to prevent over heating. I have used that set up for many years, a little more complex in my case (temp control is kinda what I do for a living) but it's very stable. Reality is it depend how sensitive your fish are to fluctuations. If your that anal you could use a pair of any sized heaters via a pid controler for no fluctuation at all, bit silly but if you got cash and a desire....