Again, which is better?

Depends. As a spellcaster, Paladin/Sorcerer is much more powerful. The Sorcerer has more versatility than the mage, gets more castings per day, etc. The Added bonuses from the Paladin (just one level is enough, to get the save bonuses) comes at almost no cost.

The Rogue/Wizard is different. A couple of levels in rogue (or maybe just one?) at first would give you a huge number of skill points to distribute in both rogue skills and wizard skills (as cross-class). Leveling later as a wizard, you have more skill points than you need (because of high INT) and can spend the extra points in the rogue skills that have now become cross-class. With high DEX, the modifier is high enough to ensure success most of the time. So you practically have a full mage with all the thieving skills you need.

Personally, I think both are must-have :)

I generally have both.

Paladin[3]/Sorcerer[x] has some amazing saves, is immune to some of the nastier effects that come your way and can blow up an entire room-full of enemies while they are still wondering who did this. Its great to have a sorcerer as you then dont have to plan you every battle. Just throw anything you want till the enemy is done with. Not possible with a mage.

Rouge[2]/Wizard[x] is a more versatile charecter than the former in the battlefield. Whereas the sorcerer is basically an arcane blaster the wizard can be either a ranged speciallist or a decoy along with playing the disabler for your enemies. his large number of skill points means that he will be doing the most tasks between fights and can hold his own when attacked.

I'm currently using a Rogue 2/Wizard X (currently 4). He is fun to play because I also have a Fighter 4/ Rogue X (currently 2). I send in my main Rogue and set her up for a backstab attack and then hide my Wizard and set him up to blast the enemies while my Paladin and Cleric come in to clean up and keep the baddies off the Wizard.

Race also can come into play, personally I love drow which makes making a multiclassed sorcerer have a exp penalty.

If you want more then two classes with mage as primary and no exp penalty consider the options:

Pal(x)/Sor(x)
Human, Half-elf, Wild elf

rogue(x)/wiz(x)
Human, Half-elf, Moon elf, Male drow, deep gnome (illusionist only).

For rp reasons I like having my mages have natural magic resistance, hence drow and deep gnome are my normal choices. Also none of the sorcerer options start with 20 charisma, but the drow starts with 20 int.

Xefiel

You forgot the aasimar.
His favoured class is paladin, so an Aasimar pally[x]/sorc[x] does not get any multiclass penalty.
And he can start with 20 Char.
A wild-elf is useful if you intend to mix-in two classes or more with your sorcerer, else the aasimar beats him hands down.

...I like having my mages have natural magic resistance, hence drow and deep gnome are my normal choices.Ditto, that's why my Rogue 2/Wiz X is a Drow. I also have a deep gnome Cleric (Stormload of Talos). I'm keeping her pure so as to not recieve any XP % penalties and she does quite well on her own. Unforunately, spells are quite scarse in the Prologue and Shargelene Bridge unless you buy them. I'm trying to not buy anything and then buff my Wizard up with spells when I get back from the bridge.

I didn't forget Shrikanth, I specifically said if you want more then 2 classes with mage as primary.
Aasimar pal/sor is only 2 classes.
Under your point you could say the rogue/wiz could also be any race that has rogue as favored class, which adds 3 more choices for him. Either way he has more choices, even if they aren't the best character. This was the point of my post.