You can either look for something more premium, but more expensive or less expensive bit lower quality. Generally you get what you pay for.
On the more premium side of things you have Eheim. An eheim pro 5e would be their equivalent to an FX4.
IMO Fluval and Eheim offer the best options for large canisters.
On the more budget side you have a Chinese manufacturer called Sensen that markets their products under different names in different locations. All Pond Solutions in the UK. Sunsun in the US. They also market under the name Polar Aurora. Their closest equivalent to an FX4 would be the All Pond Solutions 1400EF. Sorry I don't know the Sunsun model number for that. Sunsun filters are very popular with large scale hobbyists where value for money is important.
But a large canister is a large canister. They will be heavy to move and with your sizable aquariums, unless you plan on setting up sumps, canisters are probably your best option. You could go for 2 smaller canisters, rather than 1 bigger one. So say 2 x 307s or 407s instead of 1 x FX4. Sumps would definitely be easier to maintain.
You could consider a small pond filter, which was the preferred option for large aquariums before Fluvals FX range went to the market. But I don't really know where to direct you there.