Strava or Garmin or watts meter:

I have a Garmin and use it for mapping but rarely use it to compare times. I ride a regular route and I compare average times.

I have to say that a the Garmin is ok but if it dies I will go with my I phone with a battery pack. The inter-phase is much better with the I Phone and the cost is much much less.

I will probably never get a watts measure seems like extra weight and huge cost for little gain.