Depends on your viewpoint really.
Rebel fighters:
1.) have shields and possibly thicker hulls. This makes them harder to destroy.
2.) They carry warhead launchers. This gives them the ability to not only harm larger craft, but also a one-hit kill on any fighter.
3.) THey have hyperdrive - increasing their tactical flexibility.
4.) supposedly (according to the RSB) Rebel fighters have much better long range detection capability.
TIEs may seem to lack in alot of areas, but lets consider:
1.) They are much lower mass than X-wings, with superior engine performance. This gives them substantially greater speed/acceleration and agility.
2.) They have superior targeting systems (ref: SWICS - original trilogy) than the Rebels. Presumably, this also means their EW/ECM systems are superior, but not neccearily (but it seems likely)
3.) Their weapons are at least equal to, if not superior, than Rebel guns in terms of firepower and range (especially with their EW advantage) - it was indicated that to get comparable performance, X-wing lasers ran at nearly their maximum safety limits - presumably this means TIEs have better weapons.
In some ways, though - TIE weapons are clearly superior. They can fire and track off-center from the ship (giving them a much wider angle of fire) and the 2 lasers on a TIE fighter could match the four lasers on an X-wing for rate of fire. Presumably the "quad gun" interceptors and Avengers would be at least twice as fast as Rebel guns.
4.) TIEs are very compact targets with narrow profiles from head-on - and from the side, the only increased surface area are the radiator panels, which aside from being armored, are not neccesarily vital targets
Contrast to the bulkier X-wings, which require substantially more space. This allows capital ships to naturally carry more TIEs than Rebel Starfighters (roughly a 2:1 ratio, it would seem.)
5.) It may be possible that TIEs have soem low level form of ray shielding (at least to protect the pilot and vulnerable systems) - this might offer some limited protection ot the ship.
It becomes apparent that the notion of "Advantage/disadvantage" depends on your doctrine. The Rebels have a huge production/personnel disadvantage ocmpared to the Empire. By focusing on quality over q uantity, they can insure that they conserve what little resources they do have from destruction. Their fighters are also designed more clearly for long-range, independent operations (Hyperdrive and better sensors) as well as engaging different targets (the inclusion of torpedoes and shields.
The Empire, however, can not only afford attritional losses (which makes a cheap to build and mainttain starfighter practical), but also numerical superiority, which means they can afford to fling MORE fighters at the Rebels as well. They also specialize their fighters - TIE fighters are non-jump capable (capital ships can do this), dedicated to specific tasks (TIE fighters engage fighters, bombers provide missile support, - there are numerous other TIE variants - fire control, recon, etc.) and so forth.
One must also consider that the emphasis on superior weapons, superior EW and targeting, small profile and high agility emphasize that the TIE fighter is designed for long-range engagements and to avoid being hit.
The oft-claimed "2 km" range for Rebel fighters is a visual range for the most part, and as we know from Han Solo at Star's end, close parity on EW/sensor systems can render long-range engagements unreliable, making visual ranging more practical. Presumably, in the post-Endor enviroment, the Rebel either upgraded their sensor/EW capability to Imperial standards, or Imperial sensors became less effective (with the logistical and production problems the warlords may have faced.) The Rebel Sourcebook also goes into some detail as to the preference of close-range fighting over long range between most SW vessels (at least from the REbel side of it)
If one couples the "long range targeting" doctrine with the "numerical superiority" advantage the Empire enjoys, things make more sense. In a single figh ter versus fighter basis (or small groups, say flights and maybe squadrons) - X -wings would clearly be superior. But in larger battles, where you get multiple variants working together (TIE Fighters/intereceptors to engage directly - TIE/fc fire control ships providing supplementary targeting data, TIE Bombers providing long-range missile fire.) TIEs can clearly not only bring greater concentrations of firepower to bear, but also from a far longer range (and maintain that range).