I find murlock is good enough for golden portrait farming.
Here is my result.(In Standard Rank 20 and without any files there)
Deck
### Murlock
# Class: Warlock
# Format: Standard
# Year of the Mammoth
#
# 2x (1) Flame Imp
# 2x (1) Grimscale Oracle
# 2x (1) Murloc Tidecaller
# 2x (1) Voidwalker
# 1x (2) Blowgill Sniper
# 2x (2) Bluegill Warrior
# 1x (2) Dire Wolf Alpha
# 2x (2) Murloc Tidehunter
# 2x (2) Rockpool Hunter
# 2x (3) Coldlight Seer
# 1x (3) Darkshire Councilman
# 2x (3) Murloc Warleader
# 2x (3) Primalfin Lookout
# 2x (4) Gentle Megasaur
# 2x (4) Seadevil Stinger
# 2x (5) Doomguard
# 1x (5) Finja, the Flying Star
#
AAECAf0GBNkHtKwCrbwC474CDTDFA9sD/gP3BOMF0AenCMII870CncICscIChsQCAA==
#
# To use this deck, copy it to your clipboard and create a new deck in Hearthstone