fluffy and dense bud of the same strain?

Different growers.
Sounds like someone is harvesting early.

 

Might be the lower buds (larf) on the same plant. Usually classified as "B" grade buds. Normally lower in cannabinoids...but often negligible.

 

The better one is the one you prefer. Period.

Strain names don't reliably mean anything so even though your dealer and the dispensary call something the same, it has no bearing on what it actually is. I recently bought some cannabis at a shop and after enjoying it, I became interested in growing it. Looking up the strain name came up with results that described bud that was drastically different than what I purchased.

Growing out two seeds of the same strain from the same breeder can result in two pretty different products. It really is difficult to impossible to reliably get the same product from different places.

 

What do you mean by better? Different varieties and different grow methods result in different products.

Folks who grow for business tend to grow fast flowering, dense, high volume varieties because it makes them more product hence money per grow. Classic indoor growing varieties were cultivated to product these types because it is/was a black market business. Thus folks think they like the rock hard bud because the best/strongest bud has often been rock hard. In truth you can grow awesome fluffy bud. Personally I tend to prefer the varieties I've grown that result in fluffier flowers.

Your dealer might not have very strong lighting or isn't using the light very effectively. Not enough lighting results in fluffier bud but that's not the only factor.