We have a similar sized tank and find a 100W more than enough.
We did try a Hydor 200w inline heater, though really twice the size needed for a tank your size. You need to get the right model as some have 12mm fittings, some 16mm.
It worked ok, but for us in a small room , as it was switched on and off by a mechanical relay we found it very annoying as it really echoed in its plastic case and switched quiet often due to its oversized element.
Aquael do a similar inline heater but 300w seem to be the smallest size, so the problem would be worse unless they use an electronic switch instead of a noisy relay ?
There are quiet a few Ytubes on making your own inline heater using a standard in tank heater.