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Which fluval are you looking at? I personally don't like most of the Top Fin products. They are generally bottom of the line when it comes to quality (though they are priced fairly cheaply as well, usually). Fluval on the other hand makes some high quality gear (usually), though, as you have pointed it, it is often more expensive.
I prefer titanium heaters. Glass heaters have a propensity to explode from time to time. But, if these are the only 2 you are interested in, I would chose the fluval over the top fin.