the 150 gallon is the better size.
but there is quite a difference in build quality between AGA and Perfecto.
I went through the same questions when deciding which brand to buy for my 150g (6 foot). I chose the AGA.
first thing to notice is that the cross brace on the AGA is much thicker and beefier than the perfecto one, which is flimsy.
secondly, the silicone work on the AGA is thicker.
finally, check the glass thickness. some AGA tanks use thicker glass than the same size Perfecto tanks. not all, but some.
for example, an AGA 120g 4x2x2 weighs 191 pounds according to their specs on their website.
the Perfecto version of the same tank only weighs 144 pounds.
the AGA size is almost 50 pounds heavier.
the significant difference is because the AGA tank is made with 1/2 inch glass, the Perfecto version only uses 3/8" glass.
I don't like it when they skimp on glass thickness because its cheaper..
take a look at the 150 Perfecto, and if it looks nice and thick, with good silicone work, go for it.
if you think it looks not that great, go with the AGA.
with big tanks, you want maximum build quality.