Best Clan tank, hands down, before the Jihad is the Morrigu & Morrigu (Laser) built in '64. Longest reaching weapons for when you get pillbox'd, original has LRMs for significant IDF power & can start fires to cover its withdraw using the SRMs. Oh yeah, the original has ECM to keep pesky electronics in check. The (Laser) might have less armor, but its still a solid shell.
Before that the best tank in the Clan inventory? Royal Von Luckner- 2 LB-10X, LRM10 w/ArtIV, 4 SSRM2, SPL, and 11 tons of armor.