I`m in PW452 (year 1966), till 1958 I used meanly Lockheed L-1049, L-1049G, Douglas DC-7A, DC-7C & Ilyushin Il-18. After that I switched to 707 & DC-8 family. But be carefull, or the maintance fees will hound you. The old prop planes are usefull till about age 5.0, but the newer jet planes are more expensive and need replacing around 2.5yr. I now use a mixed fleet of Boeing & Douglas widebodies (+/- 180 Pax), for routes over 10Mil pax. Routes between 5 & 10 mil pax are flown with narrowbodies (Convair 990, Vickers VC-10, (707)-720 & +/- 100pax a/c on the short hauls).
In hindsight I made the mistake of flying 707-120 on 1.0 freq from airports 5mil pax and up. If I had to do it again (and I shortly will in PW1474), I would advise to use the 707 & DC-8 family A/C only on from about 3000nm and up on 0.5 freq routes from airports with minimum 10mill pax. Use the Il-18 on the shorter routes with 1.0 freq till the Tu-114 comes out. Then use the Tu-114 on 0.5 freq.
Another good guideline is to:
1 never buy aircraft over 300pax.
2 never buy aircraft over 200mill.