Safer in the unit, as he can't be shot at with BS weapons and gets 4+ look out sir. Outside the unit he is less safe, but can potentially move further forward so the flying move can get behind lines. Just depends on how the board is set up, and the enemy shooting capabilities etc. Use your best judgement, and remember you can always join/leave units.
To the OP, I guess I'm the only person who doesn't like Lore of Life on their Slann. Everybody is talking about how it's the optimal choice for LM, but so much of that lore is based on being able to get off a ton of RIP spells. I really don't care for how the Lore handles. I think a lot of this has to do with the fact that I don't take Temple Guard, but so far in my playtesting, this is how I rank the Slann Lores: 1. Light - This one's the do-all for the Slann. Net is almost always useful...even chaos warriors fail it 1/3 of the time. Light of Battle makes a unit unbreakable for a turn. Speed of Light and Timewarp are completely destructive if either(or both!) are cast onto saurus. Pha's protection is pretty useful, though not a game-winner. Most importantly, however, the two missile spells, Burning Gaze and Banishment, are tremendous. Shem's burning gaze gives you flaming attacks, and when upgraded, goes to S6, so it can wreck up hydras and the like...while Banishment scares the hell out of anything with a ward save. Also, VCs, TKs, and CDs will hate you when you're rolling 2-3d6 on them. Light's my go-to choice. 2. Fire - Of all the Lores, I think Fire is the most underrated. I even underrated it before I tried it. I LOVE Fire. It's great because of focus of mystery for all the spells, and focused rumination for additional dice pair tremendously with the additional d3 roll that the lore gives you if you've already cast on the target previously. This lets you absolutely decimate a unit per magic phase. Almost all the spells can be extended to 48", casting costs are quite low, and you wreck anyone depending on regen. FLAME CAGE. 3. Shadow - (caveat: I haven't used this lore yet) The sig spell is an awesome hex with good range and casting cost. The Slann can get hisself out of sticky situations with steed of shadows; Pit of Shades is scary to most armies. The other spells seem pretty cool, but this is all theory at the moment. 4. Metal - I love this lore when it's working, however, it can be rendered nearly useless versus certain opponents...and that sucks. The Final Transmutation is freakin awesome, and is almost always useful, however. 5. Beasts - A pretty fun Lore. The Amber spear can wreck big monsters, and the augs are some of the best in the game...but short range. Also, it has strangely high casting values(unless you're casting onto a beast of some sort). 6. Life - My biggest complaints with Life are that it's mostly short range support spells, and it relies on RIP spells to get the most out of it. I like the buff spells, specifically the Toughness upper, but it seems quite limited to me. 7. Heavens - This guy is hurt most by the fact that our other casters are required to take it. It's actually an alright lore, as it has higher strength than most others, and the comet is quite hilarious...it's just too unreliable for me. 8. Death - So many of the spells have such a low range, that it's VERY dangerous to try casting them. Also, a lot of these spells punish low I models...which is basically any of our expensive units.
First post, but I have been playing Lizardmen in a competitive environment for a while now, I figure I would chime in here. Lore of Life- At first glance, it seems like a fantastic lore, and it is. But it is not all that and a bag of chips for a lizardmen player. Most players these days will run two blocks of saurus and a temple guard unit. Every spell in life is fantastically powerful, but only for a single unit at a time. This was my default Lizard lore, until I started experimenting a bit. Lore of Light- This is my new go-to lore for Lizards. By situating my two Saurus blocks around my Slaan block, I can give my entire army huge buffs. Pha's Protection + Speed of Light means that almost everything in the game is hitting your entire army on 6's, which is far better than T8 for a single unit in most cases. Plus, you are now WS 10 I 10, which means that your entire army just got a massive offensive boost. And now War Machines miss 50% of the time. These two spells together make your entire army ridiculously hard to kill. Add in Timewarp for +1 A and ASF, and now you have re-rolls plus more attacks on the first rank (which is a massive offensive boost). My saurus blocks on average got 24 attacks (6 wide), which meant that there would be about 8 wounds vs T3 armies. With light, I get an average of 18 wounds. This is a massive difference, especially considering that most armies just went from hitting me on 3's to hitting me on 6's. Plus, the Net is excellent at shutting down enemy troops, especially enemy casters. Both direct damage spells are excellent, and the leadership spell is great for making sure that the one losing fight you have on the board doesn't break away. All in all, I find Light to be far more useful than Life ever was. I will go into more depth with Lore of Death later, as I also consider this to be a ridiculously strong lore for Lizardmen.