Forget about Dash for a minute, I really want to learn. I have some Dash but this isn't important in my view. I am a totally avg guy that knows just the basics, and I think that Dash has (and actually is developing) some unique features. Monero isn't, apart for not delivering; just nothing that I see good from a mktg/finance perspective.
But I may be wrong. Just tell me why, I want to learn
Basically Monero relies on the protocol or the math to ensure privacy and Fungibility. At this point it's really the only viable currency with those unique attributes.
It also addresses other concerned like building around planning for hard forks so it's not scary & dynamic block sizes.
The development has been slower as Ring Signatures required a new code base (unable to copy bitcoin's code base).