They are generally very nice rifles. The Diana 48/52 series are a bit heavy but can compete very well for accuracy against non sidelevers. The recoiless 54/56 (do I remember correctly?) are a good design but also on the heavy side. Many say you have to short stroke the 48/52 to get acceptable performance / shot cycle at <12 ftlbs, but I have shot very sweet examples in standard format.
The Air Arms series of sidelevers from yesteryear ... Mistral, Bora, Camargue, EX88 were highly regarded when they came out and I remember the magazine reviewers positively drooling over them.
Cheers, Phil