I recall having a rogue with longsword 1d12 (+ pretty small bonus) x5 damage. Swinginess extreme!
Five times the fun!
But that's not real reason I prefer sneak attack . I do that because it is empowering on a rogue, lets you attack with quirky personal weapons, a sap, an unarmed attack (you don't even need the feat as they get no AoO if they are flat-footed). Sure taking greatsword proficiency is cool as a rogue, but I like that the weapons selection doesn't really matter a few levels up.
IIRC you couldn't backstab with a greatsword (but can sneak attack with one).
I'm all for diversifying weapon selection. The things I dislike about sneak attack (some of which may be true of backstab as well, to be fair):
*Catching someone completely defenseless is not much better than flanking them. Denying someone their Dex bonus to AC can entail a great deal of strategy, planning, and skill on the character's part as well. Flanking is basically just "that thing characters do automatically whenever there are two of them nearby".
*Useless against many monster types. (I don't recall if that was true of backstab or not)
*High damage values for small/weak characters. An extremely skilled halfling fighter with a dagger still probably struggles to break 10 damage. An extremely skilled rogue can easily do 30.
*Low damage values for big/strong characters. If a storm giant rogue sneak attacks you, the extra damage dice are likely close to irrelevant.
*Damage is per strike and opponents don't get any better at defending themselves after the first one, encouraging characters to use TWF or otherwise load up on attacks. This is exactly the opposite of my image of a rogue who is focused on making each strike count and strikes decisively.
*Fails to provide an attack bonus. Sure, this is patched in several ways, but SA can still be swingy in the wrong way because it does high damage, but rogues often miss.
*Fails to model the decisiveness of the attack. Hitting someone really hard is not the same as hitting them in the right place (vp/wp allows this distinction to be modeled better).
*No real mechanic for rewarding untrained, non-rogue/thief characters who catch someone off guard (which is true with backstab as well).
Perhaps most importantly, as a player I find it much more enjoyable to multiply damage than to roll a bunch of square d6's. It makes rogues/thieves different. It's fun.
***
For me, creating a satisfying rogue required instituting vp/wp (and associated changes to crits) and splitting SA into four abilities. One that gives a small attack and damage bonus in flanking and backstab situations. One that improves crit range, and another that improves crit multiplier, only in backstab situations. And, finally, one that grants bonus damage dice, again, only in backstab situations.
I really despise 3e SA as written on a lot of levels (even though rogue is conceptually my favorite class, and one of the better PCs I ever played was a rogue way before all that houserule stuff).