Over the past few years, the music game category has exploded. Lately, you can't go a week without hearing an impressive statistic tied to Rock Band or Guitar Hero. For instance, Activision Blizzard CEO Bobby Kotick recently said that Aerosmith has made more money from Guitar Hero: Aerosmith than they have from any of their albums or tours. Meanwhile the success of Rock Band has rocketed MTV Games to become the number five game publisher by revenue. And the best part of all? Anecdotally, I can say that music games are a great way to get parents, spouses and other casual gamers to rock out on an Xbox 360 or PS3.

Ozzy Osbourne's music and likeness is featured in Guitar Hero: World Tour.

Rock Band 2 ups the ante with more songs and customization.

Battle of the Bands mode in Rock Band 2 includes daily challenges.

In the past, the idea of renting a music game hasn't made a lot of sense because of the hardware peripherals. That changes this year, however, because now you don't have to buy new instruments to play either Guitar Hero World Tour or Rock Band 2. While new instruments are available, both games are completely cross-compatible with each other's peripherals. So you can use your Rock Band guitars for Guitar Hero, or your Guitar Hero drums for Rock Band 2!

Rock Band 2 was first out of the gate with the Xbox 360 version in early September (the PS3 version follows in October, with Wii and PS2 in November). Last year Harmonix blew everyone away with their full band experience, and this year's game refines that concept as opposed to completely reinventing it. New modes include a drum trainer, an online Battle of the Bands mode with daily challenges, and fun tweaks like a No-Fail Mode, and a Performance Mode where you have to play through a song with no notes on the screen! When it comes to the track list, Rock Band 2 has an impressive lineup, led by songs like AC/DC's "Let There Be Rock," the first track of Guns 'n' Roses long awaited Chinese Democracy called "Shackler's Revenge," and tracks by bands including Foo Fighters, Soundgarden, and The Who.

In the other corner is Guitar Hero: World Tour from Activision, due out at the end of October for every platform. The strange irony is that Guitar Hero was first created by Harmonix, the developer of Rock Band. But now it is made by Neversoft (the company behind the Tony Hawk games). As for World Tour, it clearly takes its inspiration from Rock Band by adding drums and vocals to the core Guitar Hero experience. The hardware is also slightly modified, with the guitars featuring a touch-screen slide bar and the drums including five pads (two of which are elevated cymbals). The silver lining: If you plug in a Rock Band drum set the game automatically adjusts to using four pads.

As for the core of the World Tour experience, the game features an impressive lineup of its own, including 16 songs the two games share in common like Bon Jovi's "Livin on a Prayer" and "B.Y.O.B." from System of a Down. Other songs include tracks by Coldplay, Linkin Park and Tool (a band which still won't let its music on iTunes). One added twist is that rock legends like Ozzy Osbourne, Sting, and Smashing Pumpkins' Billy Corgan appear in the game as playable characters. And if you want to become your own rock god you can fire up the game's creation mode, compose your own music, and then upload it online to the "GH Tunes" service. How long will it be until we see a #1 song on the Billboard charts composed entirely in Guitar Hero?

Soon we may even see big-name musicians composing songs exclusively for Rock Band and Guitar Hero, and who can blame them? It's widely acknowledged that these music games are helping reinvent the music business, especially given that downloadable add-on songs are selling like wildfire. Rock Band has released at least a couple new tracks every week, and this fall, full albums from bands like the Red Hot Chili Peppers and No Doubt will go up online as well. For Guitar Hero, Metallica recently released their album Death Magnetic alongside the CD release. The bottom line is that the tracks on the game disc are just the start of the experience. By the end of 2008, Rock Band is promising it will have more than 500 songs as part of its virtual library.

Which game should you rock out to first? You really can't go wrong with either one, especially now that you aren't forced to make expensive instrument purchases to enjoy the experience. Rock Band was first with the full band experience and therefore gets the first mover advantage, while Guitar Hero's composition mode adds a YouTube-like twist to this rapidly expanding genre. So why not add both to your GameQ and set up your own Battle of the Bands this holiday season?