If this is the first time you are playing an arcane caster, I cannot stress enough how much more hassle and paperwork the Wizard is.
Seriously, go Sorcerer. Read Solo's Guide, which has a LOT of 'Core Only' ideas.
Sadly, sorcerers can't go Loremaster easily, due to the requirement of having SEVEN different Divination spells and FOUR different feats.
There really isn't a decent PrC for sorcerers in Core. The Theurge is actually not looking... too bad. Particularly not if you pair it with Spontaneous Divine Casters
from the SRD. Bunch of spontaneous spells available to you. Choose your Domains carefully, because those spells are added to the Spells Known. If you grab the Healing domain and the Liberation
domain, you pick up all your healbot spells gratis, so you can focus on grabbing useful spells to compliment your sorcerer spell list. Like picking up Protection from Evil on your Cleric list, and picking up Hold Person a spell level sooner.
True, it isn't perfect, you will never cast 9th level spells, but at least you will have a broader versatility. If that's not your thing, go Sorcerer16/Archmage4. It sucks, but hey, it's better than nothing.