I constantly hear recommendations by DDO players to take Con over Dex for a caster. Having played Pen and Paper for so long and having always had more Dex than Con with my Wizards and Sorcerers, I absolutely had to get all the information first.
A common argument against Dex casters is the non-existence of the Ranged Touch Attack. Also, the Reflex save gained from the Dex only assists Sorcerers. (Assuming the Wizard takes Insightful Reflexes)
The _most_ common argument that I hear is that Wizards and Sorcerers will not get enough AC at higher levels to matter, so there is no point in wasting points in Dex. This is where I disagree...
32-Point Starting Stats: (Elf or Human)
Str - 8
Dex - 16
Con - 14
Int - (18 for Wizard, 8 for Sorcerer)
Wis - 8
Cha - (8 for Wizard, 18 for Sorcerer)
You'll get up to 24 Dex by level 20 through Dex equipment and/or a Tome (26 for Elf with Dex enhancements). Cat's Grace can supplement your Dex at lower levels if you so desire.
Armour Bonus:
+5 Mithral Chain Shirt w/ Ritual - 10 AC, Max Dex Bonus 6 (For the Elf option, as you'll need Elven Arcane Fluidity enhancements for 0 Arcane Spell Failure)
OR
Icy Raiments w/ Ritual - 5 AC
Amored Bracers - 8 AC (Superior to the armoured option, but harder to obtain)
Shield Bonus:
Shield Spell - 4 AC
OR
+5 Light Mithral Shield w/ Ritual - 7 AC (More than the spell but takes up your off-hand)
Dodge Bonus:
Dodge Feat - 1 AC
Chattering Ring - 3 AC
Deflection: 5 AC (Protection)
Nautral Armor: 5 AC (Barkskin)
Insight: 4 AC (Shroud Crafted)
The total? Up to 55 (56 for elf)
After adding Displacement and Stoneskin, you are just a burly (if not more) than the other armoured beasts (or rangers) you'll see out there.
Wizard would probably be the better choice in this due to the extra feats.
~Xanndros
Note: You will not need to take proficiency with armour or shields unless you intend on using a weapon for damage, but the painfully low BAB of Wizards and Sorcerers makes this an increasingly worse idea the higher you get in level.