[Naniwa]

Of the following two which one has a better sound quality. I use headphones
Titanium HD
http://www.newegg.com/Product/Product.aspx?Item=N82E16829102033

XFI USB HD 
http://www.amazon.com/Creative-Sound-Blaster-System-SB1240/dp/B004275EO4

 

[ROBSCIX]

The Titanium HD has better components.

 

[PurpleAngel]

I would assume the Titanium HD has the better sound, best price right now is $140.

 

[NamelessPFG]

The Titanium HD has the EMU20k2 DSP, so it has all the gaming features the X-Fi HD USB doesn't. That alone means better sound quality in games with hardware sound acceleration (EAX effect support).
 
As for actual analog output quality, I don't have enough information to say one way or the other, mostly on the X-Fi HD USB end of things since I don't own one.