The Lore of Life seemed to be the hot choice for a few months at the start of 8th, and while I agree it has lots of good stuff in it, its popularity has really died down in favor of Light and Shadows among the better players in the metagame where I play. Good protection from miscasts with Throne can be a blessing if you bunker your Slann in Temple Guard and like to throw lots of dice at Dwellers. My biggest concern is most of the lore is mediocre or situational. The loremaster discipline for a Slann with Life is almost a necessity to avoid having your magic phase handicapped if you don't get one of the spells you really want. Dwellers works great against majority toughness 3 armies sure, and Flesh to Stone is nice (just don't cast a Throne-boosted version against an army with a Screaming Bell that has a chance to wipe out your T7+ models), but the rest of the lore leaves somethng to be desired in my opinion. Along with the magic missile and movement deterring spell, the signature spell is mediocre at best. I also think Regrowth is highly overrated. Getting models back is great, but it is very limited (you don't suddenly get to act like a VC army) and usually takes a good number of dice. Again, I'm not saying the lore sucks, I just don't like its limitations.
The Lore of Light is my personal favorite for Lizardmen. First, it hugely supports the major weakness of your Saurus units (whether they be Warriors or Temple Guard), which is low initiative and movement, by offering spells that can either give initiative 10 (and WS10 too), or ASF with double movement and an extra attack. If you are facing someone with the Shadow or Death lore and are expecting templates forcing initiative tests, then Speed of Light is your best friend. Moreover, the rest of the spells can also be very good. Both magic missile spells are flaming, and Burning Gaze can be boosted to S6, giving you a great weapon against Hydras/HPA/Trolls with high toughness and regen. The Net spell is also a great tactical weapon to help you pick and choose your fights or gain a tactical advantage. The ability to impair your opponent's ability to hit you is also a very strong advantage. The only situational spell is the leadership one.
Shadow is similar to Light in that there are mainly spells that debuff your opponent rather than help your troops counter a weakness. It's big selling point is offering Pit of Shades if you face a lot of other low initiative armies. Mind Razor is great, but Lizardmen don't have the blatant need for added strength they way they do for initiative.
Anyway, those are my thoughts on Slann lores (Heavens and Fire could also be useful too though depending on how you like to play). The most important thing is that it works in your metagame and makes it fun for you.
