That is a tough choice for me, but I'd say my trusty old FWB 124 Deluxe, which I bought new from Beeman's circa 1980 (they were at 47 Paul Drive in San Rafael.) My 124D came with the aluminum trigger, and judging from the serial number, is a late-production rifle. I shot my FWB 124D several hours a day and have always maintained it. It's still in immaculate condition, although I sold the Beeman Model 66 2-7X[32] it originally wore in it's "Beeman Professional Scope Mounts" decades ago. The Model 66 had needed warranty work, and after Beeman warrantied it I sold it and replaced it with a Leupold Vari-X 3-9X[33] EFR. My 124D was my first quality air rifle and I have many fond memories shooting and hunting pests with it to sell it.
IF, OTOH, I didn't own my FWB 124D, my never-sell airgun would be one of my three (3) R1s'. R1 Laser MKI in .177', a .20 matte hard chrome Project (think R1-AW but matte hard chrome instead of nickle plating), and a gas-spring powered .20 R1 Carbine in a "Straight Classic" walnut stock. This stock has a shadowline cheekpiece and is reminiscent of a Gary Goudy stock. I had Dave "Triggerman" Slade install the Gas Spring many years ago. I love the smooth cocking and firing cycle with that "thuunk". It wears a Leupold 4.5-14X[40] Vari-X III with Tapered Adjustment Knobs & German #4 Reticle in Beeman Sportsmatch Rings. It also has a Jim Maccari Polished Steel Trigger Guard and Brass Venom Trigger Blade (wish it was a Rowan Engineering Extra Setback). I still need to send the stock to Sherry Abraham for a wraparound borderless checkering pattern though.
Keith