Both models would be suitable for a 90 gallon tank, though if you are running a planted tank, you may need more flow rate (or a 2nd filter) to create sufficient circulation around the tank and reduce dead spots.
The classic models have been around for a much longer time and also cost less, hence more people have used them before.
The Pro3 models are newer and cost more, but they come with lots of additional features like inbuilt safety taps, self-priming, lower power consumption etc. So if you have the budget and like the features then that would be a good choice too.
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