Are steam gauges more reliable than glass panels?
Most aircraft using electronic displays have double (and sometimes triple) redundant power supplies to keep the electronics alive in cases of power failure. The mechanical gauge panels of the not so distant past did not have these same levels of redundancy built in. 

Beyond power considerations, glass panels also contain features like weather radar, collision avoidance, and navigation that further increase the reliability and safety of the system as a whole.

That said, it's fair to say that glass panels are more reliable. The funny thing is, critical mechanical gauges are still included on most panels as last resort backups.