Better backfill for Banner/Interstitial in admob mediation

Hi,
I am sure many of you must be suffering with low fill rate in using admob network standalone.
So i decided to use admob mediation in few of games/apps.

Question is, which is better banner/Interstitial/Video backfill network present in admob mediation?
Please point out based on your experience. I got as low as 45% fill rate in few apps in certain areas.

Following is the list of admob mediation networks:-

AdColony
AdFalcon
Adfonic
AdMob eCPM Floor Beta
AdMob Network - added
AdRally
ADResult
AMoAd
Amobee
AppFlood by Papaya Mobile
Appsfire
BrightRoll
Domob
Drawbridge
Facebook Audience Network
Flurry
Hunt Mobile Ads
i-mobile
InMobi
Jumptap