I am extremely partial to the Marineland Visi-therm stealths.
I have 3 of them in various sizes and I have never had a problem with overheating, breaking, fluctuations or failures of any kind.
The reason I went with the Marineland stealths in the first place was because their design seems to make more sense to me, here are the specs that I think gives them the edge over other heaters:
Aluminum body covering the heating element - This is good for two reasons: 1 it wont shatter, no matter what, and 2, related to the first reason, you will never have to replace your substrate because there is glass in it.
Auto-Shutoff - This is great for those large water changes, if the heating section is no longer submerged it will shut off automatically, this means no more replacing heaters because you accidentally burned yours out while doing a big water change.
Accuracy - Guaranteed accurate to 1 degree. Says it on the box, and from my experience it is true.
Fully Submersible - You just stick the whole thing in the water, dont need another hole in your hood.
They do have their Cons though:
No light - There is no way to tell if it is on or off, I learned to live without this. It does make an audible click when it turns on/off which scared the crud out of my until I figured out what it was
It can break your tank - since it is aluminium, if it drops onto your tank floor, or smacks against the glass it will probably break the tank if you hit hard enough, however if you just make sure not to swing it around inside your tank you should be fine....
Cost - These are more expensive than most heaters. I cringe every time I buy one for a new tank, however, I have also never had to replace one, and I have come to learn with fish-keeping that usually its cheaper in the long run to spend more for a quality product.
Hope this helps!
one less problem to have to deal with.
