Loaded question. You will get tons of different opinions. What’s your budget? Is your tank eurobraced? Do you have a lid or intend to have a lid? do you mind wires inside your tank or prefer them to sit on the outside?
Myself, I have a eurobraced tank with a lid so prefer to have all my wires on the outside. This limits me to eco tech mp40’s or their cheaper clones from Jaebo.
If I were starting over, I’d look seriously at Tunze Orcas that oscillate. I think I could get away with two orcas vs the 3-4 mp40s I now run.
Oh, also do you run any kind of controller such as apex or hydros? That would also determine which ones you go with.