Wizard 1/Sorceror 1/Warmage 1/Cloistered Cleric 1/artificer 1/beguiler 1/druid 1/warlock 1/Spellthief 1/ with 8 in Con ends up (if going by the official rules) somewhere around 30 around level 10, only first level spells, 1 BAB and minimal AC. Will saves are through the roof though... However by that point, it should be easy enough to one-hit kill them with a spell targeting either a fort or a ref save, as those will be pretty pitiful (ref is probably the best to target, as cloistered cleric and druid both give bonuses to fort, I believe). That's pretty much the best build for being the worst assuming a build starting at 10th level with point buy, as he can't melee, cast, or get enough play out of skills enough to be worth it in a party. He'll also have pretty bad MAD, needing high values in Int, Wis, and Cha. Not only that, while he is "focused" at being a caster, the overall spread and lack of coherency in casting type means post 10 he won't get much help from prestige classes, as he'll just barely hit 6th level spells at level 20 if he focuses solely on boosting his sorc spellcasting from this point on.
For a less overtly bad build, Sorc 5/Divine Soul 5/Mystic Theurge 10. He'll max out at 7th level divine and arcane spells, have little martial ability outside of his weapon focus(totally pointless unless he tries to use Divine Power, which he can't persist because he doesn't possess turning attempts he can burn to fuel divine metamagic, and he lacks the versatility a cleric has in choosing his spell list, as he has to focus solely on his few known spells, forcing him heavily into the healer role) So in theory, it's a better "hybrid" than Sorc 10/Favored Soul 10, but it still lacks focus and it doesn't really combine the two classes in a way that allows them to build on one another as opposed to serving two competing goals.
