With the new Lizardmen Army book out, I have returned to tuning my 5 separate Lizardmen armies (armies, not lists). As most, I started with thinking about Lords and Heroes and I have come up with the following in order of needs.
1. The General. This role is mandatory for all armies. First consideration is that he has to have the highest leadership of your characters. This stipulation alone means that if you want a wizard to be your general, he will almost has to be a Lord level character. Second consideration is that regardless of what army you play (though Vampire Count in particular) he must be protected at all cost. Even if you play a regular human army, many competition scenarios award extra points for killing your opponent's general. With this in mind, if you choose a fighter as your general, you will be unlikely to throw him into combat on a regular basis, making a Lord choice somewhat of a waste.
2. The Slayer. This role is essential for nearly all armies. First consideration here is that this character is designed to kill characters and or large monsters. As such, ideally he should be a Lord level fighter tooled up to fight, kill, and maim. However, a lord level character in most armies will typically will have the highest leadership and thus will be forced to be your general. Except for Lizardmen, a Hero is what you will end up with here. Second consideration is that his model should be as mobile as he can be in order to chase his prey down. A monster mount would be great but again most monster mounts are only available to Lords rather than Heroes. Finally, in the absence of characters or monsters to kill he can always hunt artillery.
3. The Battle Standard Bearer. This role is helpful for most armies. First consideration is whether you really need one or not. In order to get the best use of one, you will have to cluster your units around him. While this may not be such a bad idea, it may limit your force tactically. Second consideration is whether he will carry a magic banner, or be "inspirational" and armed for combat otherwise. Taking a magic banner will be the most traditional role but again would also make him more tactically limited. One options would be for him to function both as a "Slayer" and a BSB (Battle Standard Bearer). This combo advantage would be he would be more resilient in combat resolution and his disadvantage would be the higher 25 points cost. Regarding victory points if standard VPs are only awarded to over-running units, then this would not be a problem as he should be fighting challenges (and either winning or dying), taking on small units with easy wins, or re-rolling break tests and passing them. The third consideration is whether he can be a Battle Standard Bearer and a Wizard. Only a few armies allow this option but if possible, this would make a decent combo allowing the character to remain with the main battle line protected, inspirational, to either cast spells and or dispel them as a defensive wizard. Finally, only one army that I know of will allow you to take a General-Wizard-Battle Standard Bearer combination and that is Lizardmen. This is a great combo for a more balance offense/defense or just defensive minded Lizardmen player.
4. The Supporter. This role is really optional for all armies. The first consideration here really is whether you need to take a wizard for magical defense. This character will almost certainly be a Hero level. If you have already taken a wizard as your General, then he will be a much more powerful offensive spell caster. If you have not taken any wizards at all then it means you have gone with Fighters for your characters and might need some magic defense. The second consideration here is if you have no needs for a wizard in this slot, a fighting hero to lead/buttress a flanking force/unit separate from your slayer. Under most circumstances more troops might be better than another fighting hero.