For me, it's without a doubt, Aphrodite.
When I first got my Optimus, I knew something was amiss.
It didn't take synthetic benchmarks to suspect I could *feel* it anytime I used it. It felt artificially throttled and laggy. Performance, even for the V's average hardware make-up, didn't feel right. Virgin bloat, Inability to customize an open source OS the way I saw fit - these were all the reasons I took my first plunge.
I visited forums (XDA, etc.) and began learning.
Eventually, I found my way to androidcentral, and I checked out my options.
Aphrodite appealed to me because of philosophy behind LeslieAnn making it just as much for what it was.
It's not exciting or flashy, and I don't believe it is ever really meant to be. It's a rock-solid native Froyo based ROM for our phones. I know, it isn't OMGGINGERBREAD!!1, but for some of us, that's more than alright until it's officially released.
It was basically everything I was looking for when I originally purchased my device. Reclaimed storage, bloat removed, ability to customize - couldn't ask for a better canvas for my personal tastes of customization.
Recently coupling it with the picasticks .7a kernel (I believe the only kernel based off of the straight V source and not a S hack - How are more people not hype about this?!), my device is as good as it's likely going to get unless I can swap out CPU's
I've tried other ROMS, (probably all at this point

) and Aphrodite is my 'stock' default back up. I can't really see a reason to change that anytime soon.
Thanks to all the developers and performance-tweakers out there that extend the desire and enthusiasm for our 'cheap phones' to keep pushing forward.
Be excellent to each other.
-K