If possible, you should use 2 slightly underpowered heaters vs one so that there is a margin if one goes bad which they do since heaters are considered consumables. You'll notice this if your tank is slightly struggling to reach the set point during what we refer to as the heating season. This gives you the opportunity to replace the failed heater without panic since the other one is still working good enough to keep the tank from getting crucially cold.
I like the titanium heaters that have a wired controller vs just a straight heating tube.
I don't account for the other spectrum of failure (heater stuck on) since most if not everyone now uses some type of controller (apex, ranco etc) and the wired controller is the failsafe if you set it a few degrees higher than your controller set point.
So for wattage, again as Reef Trends mentioned, it depends on the room's ambient temperature. If you keep the tank in a climate controlled room, then two 200w titanium heaters should be sufficient but if it's in an unheated basement, then definitely go with two 300w and above IMO.