.....by far the flowmasters are better then magnaflow. Magnaflows are just cheaper made.
The offset vs. center inlet is basically performance based.
Not trying to call you out but Woah bro, I have no clue what made you think this.
After all the exhaust shops I have been to, and personal experience, they have all said that Magnaflow is all around more quality than Flowmaster, that info is even online. Also Flowmaster makes just about the cheapest mufflers/exhaust tips components on the Market, compared to all the other exhaust companies.
My Magnaflor muffler cost me $125 for my Tahoe even with a coupon code, the most expensive Flowmaster muffler (for my Tahoe)I saw the other day while looking online was $82.
Also center and offset inlet/outlet makes no difference in performance, just done to give people more option for clearance and exhaust setups.