Def is Def, no matter where you buy it. It's like aspirin. The chemical compound in aspirin is identical, no matter who makes it, or where its bought from. The only difference is size of the pill. Def is exactly the same way. It's a chemical compound that has to meet specific standards in order for it to be,... well .. DEF. Anything changed in the chemical compound and it's NOT DEF any more.
So, get the lowest price anywhere. It's all the same.
Now ... how the DEF is handled may be different. Packaged in 2.5 gallon containers might be a bit more controlled (cleaner), than dumping 10000 gallons into the back of a tanker truck and then dumping that into a tank in the ground that sits for years and years accumulating "gunk" in the bottom as age plays it's toll on the undergorund storage tank. THAT may be the only difference!
The price to package that DEF into those 2.5 gallon jugs may be a factor in the over all price too, opposed to bulk storage. That's the only secondary difference.