Basic Sorcerer/Beguiler comparison:
Spells Known: Beguiler has more of them, but many are redundant, and there are massive gaps (long term utility spells, non will based save or sucks, teleportation, etc). Also, they rarely have the best spells of any given level (though Colorspray and Glitterdust mean they've got very solid lower level combat options). Sorcerer has fewer spells known, but they can all be the most powerful spells that the campaign allows, and there are very few gaps in what's available (though a given Sorcerer may have trouble covering everything... which may not matter, as the Sorc takes what the rest of the party doesn't offer).
Adding spells known: Both can use Runestaffs, though Beguilers need UMD at reasonably high levels (DC 19+2*spell level to pretend to be a Wizard of appropriate level, can't take 10) to make use of them and must purchase them while the Sorcerer can make their own (and then retrain or alter spells afterwords). Note that the Sorcerer's access to Teleportation makes purchasing Runestaffs far easier mid campaign. Both can use Arcane Disciple, but Beguilers get far better use out of it since it would otherwise use up a Sorcerer's spells known, but Arcane Disciple does require a bunch of Wisdom and some cross class ranks for both. Sorcerers can use Mage of the Arcane Order to get access to every Wizard/Sorcerer spell, though it costs extra slots and time to do so, making it primarily suitable for utility and downtime spells only. Both can use Shadowcraft Mage.
Skills: Beguiler obviously wins here by a wide margin, though this only matters before PrCing out (of course, only a Beguiler has a reason not to PrC out).
Class features: Familiars are cute but a Beguiler could take Obtain Familiar and then use their skills with a familiar, and the other Beguiler class features are obviously far superior to the Sorcerer's lack thereof. One note is that Sorcerers can drop their familiar for faster metamagicking, which Beguilers don't have access to, and of course class features past level 5 or so don't matter much since PrCs become a bigger factor.
Racial: Both can get a lot of millage from gnomes. Sorcerers get a huge boost from Kobolds.
PrCs: Beguilers can get into Mindbender far more easily. Both can rock out with Shadowcraft Mage in obscene ways. Sorcerers have better access to the rest of the power PrCs, though, and make far better use of Tainted Sorcerer, Anima Mage, and Incantrix, mostly by having spells that can better make use of free metamagics like Persistant Spell.
So, the first part comes down to a question of what's more powerful... having a bigger number of potent abilities, or a smaller number of extremely potent abilities with a wider variety in what you can do. It's the same as the Mystic Theurge vs Wizard comparison, I'd say, except that the Mystic Theurge actually adds more variety in what you can do (like decent healing) while Beguiler actually loses general variety in favor of versitility in a few specific areas (will based save or sucks, illusions).
For the second part, I think it's the Sorcerer all the way. They're far better with Runestaffs, and while they're not nearly as good with Arcane Disciple they can make Mage of the Arcane Order do far far more. Shadowcraft Mage is incredible but probably inappropriate in most games.
For the rest, it's a tossup I'd say, once we consider the fact that Sorcerers are going to PrC out the vast majority of the time... it's only at the lower levels that the Beguiler's superior class features matter much. And who really cares whether you're wearing light armor or no armor past level 7 or so on a caster? I'd rather use Mirror Image!
So yeah, the Sorcerer is WAY ahead of the Beguiler in raw power. The Beguiler is quite strong early on when the Sorcerer has very few options, but at every level the Sorc gains many completely new options while most Beguiler options are actually just modified versions of old tricks. Is the Beguiler a great class? Absolutely. But the Sorcerer has the raw power, as much raw power as the DM will allow. And when we're talking about class balance and a system designed to help players and DMs decide what they should use and what shouldn't be allowed, more red flags should come up for a class that can churn out a bunch of different super powered options than for a class that has even more options which are mostly pretty similar and none particularly game breaking or even overpowered (except maybe Colorspray and Glitterdust at the low levels. Time stop is far less scary without Celerity, considering the level you get it).
JaronK