It's mostly a personal preference if you own both of them. If you go with .guru, visitors may experience a bit of reservation at first, but those reservations will dissipate over time as people become familiar with new gTLDs. I'd prefer to see smartphone.guru in my address bar rather than smartphoneguru.com. I'd rather see it in an ad, as well. It's more unique. Less common. More interesting. Less boring.
I don't know about you, but I suffer from a slight case of "domain blindness" (similar to ad blindness) where I don't pay much attention to the domain name anymore while browsing around, but a non-.com tends to catch my eye. That can be a powerful tool.
For example, if realestate.com redirected to real.estate, I'd be in awe and absolutely love it. And in my opinion, it would look significantly better. In all fairness, I would use realestate.com for offline advertising since people are most comfortable typing in .com domain names. For online advertising, I would use real.estate all day long.