Out of the two choices, I think the Eclipse Ti is the better product. If you are going for a SQ woofer, don't use the diameter as a reference for SQ. Smaller subs aren't tighter than large subs.
Whoever said that aluminum subs are lighter than titanium has a couple of flaws in their argument. Titanium is lighter and stronger than aluminum. But this doesn't really matter because a heavy cone doesn't necessarily make the sub "lag". An overly heavy cone combined with a weak motor can have negative effects, but that is a rare circumstance.
Now, If you are looking for the best subs available for SQ, I would look no where else than the Lambda subs. If you are running a thousand watt system or more, than the HE 15 from
www.stryke.com would be at the top of my list. Actually, for 375.00 a woofer you could get an Adire Brahma from
www.adireaudio.com that can rival the best subs for both SQ and SPL and would be clearly better than either the RF or Eclipse.