There is no power difference between the two, but running a power station with gas costs
50% more in operating costs. The plus is that it produces much less pollution. If you have any tourism, you may want to go with the gas option, because of the reduced pollution. In any case, NEVER put tourist attractions downwind from a power station! What I normally do is leave my power stations on coal, but I try to build them so any pollution from the plant goes out to sea, not over anything on my island. I use the substations to extend my power grid to allow facilities anywhere on my island to use the power. The substations only produce about as much pollution as a ranch - not hard to offset that with landscaping. Actually, I always try to put in at least enough landscaping to offset the negative beauty points of any buildings I build anyway.
A reasonably good summary, but it has some errors, omissions and some poor philosophy.
maintenance (that's a 100% increase) and cuts pollution by 50%. On one test map, the monthly maintenance charge for coal was $79 and gas was $158. Pollution and negative beauty are two different things, both effects radiated from the building. Pollution is 30 points which makes a wind shaped plume up to 15 tiles from the building. Beauty would be an offsetting effect except it has a negative value of 15 for this building. Only the pollution points are reduced. So the building has a rather ugly impact on the environment.
The Air Pollution Standards
edict has a similar effect on all the buildings in the "factory\industry" category -- increases maintenance costs by 40% (according to one map) which is a lot less than 100% (but more than the documentation indicates) and cuts pollution by 50%.
The idea of placing the Power Plant so the plume of pollution drifts out to sea was promoted early by a very vocal poster. Philosophically it's O.K. unless you have to leap-frog across a large island; then it is too wasteful in effort, time and money. Using gas and a vegetative screen is far more practical.
Being too frantic over exposing tourists to polluting (and ugly) buildings while ignoring their effect on your citizens is also non-productive. Consider, the Airport produces more pollution than the Power Plant, but most players consider it to be the facility upon which the high (snob) class tourist zone must be centered. I have never seen anyone else mention the Airport's pollution.