A client asked me to do a test of which is better: Saurus with hand weapons/shields or spears. Here's my erudite and enlightened response:
No need for a test. You have to choose between an extra rank of attacks (but not when charging) or a 6+ ward save to the front. Oh, and the spears cost extra, probably enough to buy two whole 'nuther Saurus warriors.
On the other hand, you'll probably save less than half a wound a turn with the shield save, while five attacks is likely to produce an extra wound reliably, plus peel off a rank now and again.
The question is, are you benefited more by the extra two Saurus you could have bought with the points you spent on spears OR killing X amount of enemy models.
It's a toughie. It's really a matter of getting your points back and WHEN. This is a matter of timing, folks. If you have two extra Saurus warriors sitting on the tail of the unit, they are probably going to be sitting around for two or four turns until they step up into a fighting rank. HOWEVER, they are beefing out your ranks that whole time, making sure you are 40% more likely to have an extra one at any given moment. And remember, ranks are doubly important in 8th edition: they give you a rank bonus and sometimes Steadfast.
With spears, you are out those two Saurus warriors but probably coming out a net half a point ahead each turn from killing things.
In the end, though, you have to go with Hand Weapon and Shield. Here's why: Lizardmen are an offensive army. You're probably going to be charging a lot, and especially now that infantry can get in the fight a lot faster (no march-blocking and additional average charge distance). Couple that with an army that also has Stegadons marching along, you've got to keep it aggressive.
PS- One other thing to consider: giving your Saurus spears doesn't get rid of the hand weapon! You just now have the option of fighting with spears. And since spears look better I'd definitely do my Saurus with spears!
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While I'll admit that there are many builds of a Lizardman army that can perform very well offensively, the most powerful is a defensive one, probably led by a Slann in a TG bunker for some buffs and long-ranged firepower, supported by Saurus blocks and Skinks to cover flanks etc. This army has very little in the way of a weak point because all of its models are probably going to be Ld 9, Cold Blooded with a BSB in range and hopefully Steadfast.
Units this large and powerful in any army can get pulled out of position and flanked easily by charging. I'm not trying to debate the merits of a particular army list, but I'm making the point that if Saurus are your line infantry, they need to be supported by a general and in a position where they can't get flanked, outnumbered etc. Offensively this becomes tenuous at best.