The X2 is discontinued - check out the newest reincarnation - the G30/G50/G90 range, they have fixed the weak points on the X2 - i.e. the transmitter clip, the cable connection and the battery life.
Well now you tell me ! ... Just kidding. I just looked at the Line 6 G series (all three you mentioned) and they are out of my price range, for now. The G30,G50,G90 are $299, $399, and $599, respectfully. The G90 is a rackmount version.
Getting back to the Line 6 X2 - It is $199 shipped. I like that.
I have rechargable 9v batteries, so as long as I keep them charged the night before I have a show, or charged up all of the time, then I should not run into an issue of 9v killer. I also like that the Line 6 X2 comes with 2 new Energizer 9v and not some generic brand. That gesture alone tells me that this is a company with integrity and doesn't cut corners, as far as I know.
THE SOUND - This is the real question everyone wants to know the answer to. The sound is crystal clear ! I found that the sound quality was equal to that of my $65 Mogami 18' cable. Super clean, no crackling, DEAD SILENT. I LOVE the lack of wires now. I had all the frequency response I needed. I didn't lose any signal or sacrifice tone. The box says that the 24 bit digital system rivals the sound quality of high end cables - they are correct.
THE SIZE - The transmitter is small. About the size of a pack od cigarettes. It has a clip like that of a garage door opener. It fell off my strap because I didn't know what direction to attach it to my strap. I will eventually make a little fastener, but until then, I put it in my cargo pocket or attach it to the back of my belt.
The receiver is the size of any stomp box - It's fantastic ! I placed it next to my head on top of the cab. It has a full, non slip foam bottom so it stays where you leave it. I attached a 3 ft cable to the head, and voila, I had crstal clear sound. I went to ROSS and went to the home dept and bought a small, clear plastic box about the size of the original box. That is now my "sound in a box" - "Look mom, no cables !" - I love it. Very easy...
Overall, I love this product, and the freedom it offers me both on and off stage. Having the sound quality of Maogami or Monster without the cable itself is well worth $199 new shipped to my door in two days. It is a fair price for a product I like.