Both are high quality airguns made in Germany. Diana is made by Mayer & Grammelspacher. Beeman sporting rifles are rebranded Weirauch's. Their match and 10-meter rifles are Feinwerkbaus. Most of the better quality production adult airguns are made in Germany or England, though there are some really good high end custom/semicustom guns made in the US.

I've never owned a Diana, but they have a good reputation. I bought my Beeman R9 because it had the reputation of being one of the best bang/buck (excuse the pun) airguns around. But I know a lot a guys who swear by their Dianas.

Kevin B.