I have had good experience with both Little Giant and Iwaki, but I like the Iwakis better. They are a little quieter than the Little Giants I have used (I haven't tried the "SQ" types), and are very strong. They also have "fins" on the motor so that it's like a built-in fan. The Iwakis are more durable if they run dry for a little while. I think they are worth the extra money. The advantage of using an "external" pump, not all of the heat is transferred to the water, and you can have much more powerful pumps. A submersible pump transfers ALL of its heat to the water. If your stand is ventilated, you can manage the heat much better with an external pump.
Sonny