I won't count anything that moves 6/9/x as slow regardless of era, there are too many light 'Mechs at that speed bracket i like. That speed is kinda slow, especially by the Dark Age but easier to ignore them.
The Panther is probably my favorite. Excellent looks and style, simple to operate, reasonably effective. Organizationally problematic though, as it doesn't fit in with other lights, yet i don't really want to group it with 4/6 heavies either. An Order Lance would be ideal organization for Panthers but alas, one can't get Panthers in packs of four.
Kinda like the Hollander F3, G1 and III-series D1. The G1 makes for a nice support light with its LB-10X, and the D1 feels interesting because it is different with its Ultra-10. The D2 is just a rehash of F3, so meh.
Of Clan light 'Mechs, the Cougar is the only slow one i find acceptable, not that there are many other 5/8/x or slower Clan lights. Have bit of love-hate relationship with the Cougar, was among my favorite rides in Mechwarrior IV, looks nice, but find it a bit meh for tabletop BattleTech.
Can't think of other slow light 'Mechs i like. The UrbanMech is funny but not something i actually like like, i'm not going to be voluntarily fielding it except perhaps in some scenarios.