Ok - Here's my full opinion.
It is based on the popular brands - I am sure there are alternatives to each opinion.

Glow
Good for planes up to "1.20" size.
Messy due to high oil contents.
Can be unreliable if not tuned or installed properly. (due to reliance on exhaust pressure to feed the fuel)
Larger ones use a higher quantity of more expensive per gallon fuel than the Gas equivalent.
Generally lighter than a Gas equivalent but when the extra fuel qty is considered, weights get a lot closer.

Gasoline
Good for planes larger than 1.20 size (Yes - I know there are small gassers but they are not as common)
Reliable even if not perfectly tuned or installed (Due to pump style carbs and positive ignition sequencing).
Less messy due to lower oil content.
Cheap to operate once installed and running
Requires additional power source for ignition
Greater risk of radio interference

Electric
Good for planes from 0 - "1.80" size
Depending on batteries used - can be heavy for same flight times
Depending on Battery technology used - can be a risk for charging.
Requires a good degree of technical knowledge to match everything to get the proper performance from the motor -(ESC, Battery selection etc)
Can be expensive to purchase (Mostly the larger sizes due to battery costs)
Running costs are low EXCEPT when battery replacements are considered (Especially if using LiXx technology)
Clean and quiet.


Now there are bigger electrics (like the 200 plus inch Lancaster in the UK), smaller gassers and bigger glows - these fall into the "Overlap" territory. I know guys that insist on using large (2.00 and larger glow) where a gasser would usually be used these days, I know guys that use small gassers (BME 90 is a great example) and love them. F3A is dominated by Electric and Glow but there are some gassers used quite succesfully.

Generally, I would only consider an electric park flyer, would generally consider Gas in any plane of above 8 or 9 lbs and would definitely consider glow in all the in between sizes. (And for F3A I break both rules - I have both Glow and Electric in planes around 10 - 11 lbs)

It really does depend on what your preferences are.

Do you understand any of that? If so please explain it to me, I've got myself confused now