It is usually not a question of cores but it is more like the actual video playback capability of the said Chip.
Amlogic is better supported than Rockchip or AllWinner chips. Rockchip or Allwinner chips boxes sells around a third less than an Amlogic box.
If you really want to get a cheap but worth while box. Get atleast an S905x or S912x amlogic box. Preferably with 1000Mbps Ethernet and 2GB ram and 16GB rom.
Those things sells around 55$ direct from China.
Thanks for that, I guess a better question would be for these 2:
CPU: Amlogic S905X Quad Core ARM Cortex-A53 up to 2.0GHZ
GPU: 5-Core ARM Mali-450
RAM: 1GB DDR3
ROM: 8GB EMMC
Operation System: Android 6.0
WiFi: Built in 2.4GHz WiFi
LAN: Ethernet:10/100M, standard RJ-45
HD: HD 2.0 up to 4k2k Output
3D: Hardward 3D graphics acceleration
CPU: Amlogic S912 64 bit Octa core ARM Cortex-A53 CPU up to 2 GHz
GPU:ARM Mali-T820MP3 GPU up to 750MHz (DVFS)
SDRAM :2GB DDRIII
FLASH:16GB EMMC Flash ( 8~32GB Optional )
WiFi:Built in 2.4G/5G WiFi Support IEEE 802.11 a/b/g/n/ac
Blutooth:Bluetooth 4.0
LAN Ethernet:10/100M/1000M RGMII
Note that the first is about half the price of the second.