There are certainly more than 3 cycles that many of us wish for; limiting myself to a Top 3 mine would be:
1)
Paavo Heininen
Symphony no. 1 op. 3 (1958/60)
Symphony no. 2 Petite symphonie joyeuse op. 9 (1962)
Symphony no. 3 op. 20 (1969/77)
Symphony no. 4 op. 27 (1971)
Symphony no. 5 op. 80 (2001–02)
Symphony no. 6 op. 132 (2015)
Symphony no. 7 op. 144 (2020)
Symphony no. 8 op. 145 (2021)
2) the 12 symphonies of
Wilfred Josephs Wilfred Josephs
3) the 12<12+ (?) symphonies of
Maurice Karkoff Karkoff, Maurice (Ingvar) | Encyclopedia.com
syms.: No. 1 (Bergen, Oct. 22, 1956), No. 2 (1957; Swedish Radio, Jan. 5, 1959), No. 3, Sinfonia breve (1958-59; Gavle, Jan. 10, 1960), No.4 (1963; Stockholm, April 4, 1964), No. 5, Sinfonia da camera (Gavle, Nov. 11, 1965), No. 6 (1972-73; Stockholm, Oct. 12, 1974), No. 7, Sinfonia da camera (1975), No. 8 (1979–80), Short Symphony for Symphonic Band (1980-81; Stockholm, Sept. 27, 1982), Dolorous Symphony for Strings (1981–82); Sinfonia piccola (1982–83), No. 10 (1984–85); Little Symphony (1987), No. 11, Sinfonia della vita (1993–94), and No. 12, Sinfonia semplice (1994–96)
[if asked for 5 instead of 3, my next contenders could include Irwin Bazelon and Mikis Theodorakis - but there is no shortage of other candidates]
I love the CPO label's contributions to the discographies of symphonic cycles, but I wouldn't mind subsequent alternates by others on cycles by Wellesz, Frankel + many more.