What do you want the domain for?
To build a site and get an seo advantage from an exact match keyword domain? Then if you can't get this keyword or a combination of it in another TLD, mobi would be an ok choice for development, it will do no worse than the others in search, but people may find it hard to remember.
If you want to buy the domain to resell, forget it. There are about a million mobi domains registered but they rarely sell in the aftermarket and there is an unofficial price ceiling of $5000 on even top names. It just seems endusers don't see mobi as something they want to pay for. Does anyone have a theory to explain that? Why are so many mobi domains registered? Is anyone actually using them?
.asia and .tv have maybe 200k registrations each, .me maybe 500k, but these names do sell in the aftermarket and don't have mobi's price ceiling - I see even .asia selling for $10k plus.