I have the former version of the Brown 416, which is called the 472. I can wholeheartedly recommend The Brown units. I honestly think you'd be more than happy with either cutter you choose, but I will recommend Brown.
I bought my cutter used from a friend. He was using it behind a NH TD80 farm tractor that is close to 7' wide. He wanted something to over his tracks and looked all over for the 7' Brown unit but couldn't find one used. He ended up with a Bush Hog 284 I believe is the model number. He does like it but still tells me to this day he misses his old Brown unit.
I have spoken with, and emailed back and forth between, the Brown company. They are extremely helpful and if you pick up the phone with questions they will help you out right from the main business. I recently spoke at length with them regarding their new Tree Saw, and I am always impressed with their willingness to chat with the customer and give information.
Typically the Brown units are more expensive than the Bush Hog, so if you can find them at a similar price, I see no reason not to go with the Brown.
FYI, I mow everything BUT field grass. I've mowed over all sorts of things and I don't take it easy on my mower. It is an incredible mower.
(I should mention that I don't have personal experience with a Bush Hog mower so I can't give you a truly accurate comparison)
One negative I will say about Brown though, is that they finally followed suit with every other company in the industry and stopped putting American made gearboxes on these cutters. Unfortunately, it was far too expensive to remain competitive in the market for them to continue doing so. They do still use American made gearboxes on the 6XX series and the tree cutters however.
If you want the best 6' rotary cutter money can buy, go with the Brown 672! Just be prepared to work some overtime to pay for it!