No, neither are too much for that tank. Go with a quality heater with a thermostat, and you will be all set. I would choose the 300 watt heater so it doesn't have to work as hard to keep things warm. A good heater shuts off once desired temp is reached and won't overheat the tank unless you set it too high, in which case it's your fault, not the heaters.
In the old days heaters had the problem is sticking in the 'on' position - it even happened to me once many years ago and I too boiled my fish. But I would never not use one just because of one experience - we know tropical fish need heat to thrive. This does not happen with new heaters, and especially if you don't cheap out - get a good heater and you will have no worries at all.
When using a new heater, start off at the lowest setting and gradually increase it until the temperature has reached what you want. Even if you get a heater with degrees listed on the dial, do not trust this by any stretch - do the gradual cooler to warmer method instead.