...kinda agree with the theme of the question, but sometimes a little initial direction can help new enthusiasts?
Best gun for grandpa shooting off the deck with grandkids: R7
Best gun for folks into FT: later HW77, HW97, TX200, PCP
Best gun for rich guys into collectibles: HW55, early AA guns
Best gun for low budget accuracy freaks: R7
Best gun for rich accuracy freaks: FWB300S, A380, PCP
Best gun for hunters: R9 or some variation of, or current R50S
Best gun for long range hunters: PCP with a good scope (don't know too much about these)
Best gun for collectors, low budget: early HW77, R1, HW35, early R50, FWB124
Best gun for anglophiles with money: ProSport
Best gun for folks into looking for collectible hens teeth: Falke 80/90, Annie LG54, Annie LG220, any FLZ, FWB300RT, FWB127, early BSA, etc, etc, etc
Best as first airgun for novice to buy: R7
Sorry, don't know too much about Diana, or lottsa other fine and interesting airguns, and nothing about turkish/chinese/american guns.