The lower one of course:
0x8000.
4C:5E:0C:B3:EA:E5 < 0x8000.
74:4D:28:38:AA:0A
However, if you change the priority of second bridge with higher MAC, it will be opposite:
0x
8000.4C:5E:0C:B3:EA:E5 > 0x
1000.74:4D:28:38:AA:0A
As you can see, MAC gets considered only if priority (first 2 bytes) of bridge ID is same. But it should not be same if you care about your network at least a bit. IT admin should always configure nearest switch to the main router router (or main router itself) with lower priority than default 8000 hex.
This leads us to status of the STP. You can go to "status" tab on your CCR bridge and you will see something like "root bridge ID", "root port" and "distance", which literary tells you who got elected as root bridge, which port faces that direction and how far the device is (so you can go around your network and identify the physical device)
Let me give you real-life example from my lab. It is connected like this: [mikrotik1]{ether1}---- [dumb-non-rstp-switch] ----{ether1}[mikrotik2]
Here is result from "non-root" bridge. You can see that it elected 0x8000.CC:2D:E0:AF:1D:A6 as a root bridge and port which faces towards that bridge is Ether1. (I removed rows which are not interesting for us to make it shorter)
[admin@mikrotik1] > /interface bridge monitor bridge-local once
current-mac-address: CC:2D:E0:AF:1E:63
root-bridge: no
root-bridge-id: 0x8000.CC:2D:E0:AF:1D:A6
root-path-cost: 10
root-port: ether1-uplink
Here is example from second router, which got elected as root bridge. Obviously, it does not have root port because it does not need one - it is root bridge itself.
[admin@mikrotik2] > /interface bridge monitor bridge-local once
current-mac-address: CC:2D:E0:AF:1D:A6
root-bridge: yes
root-bridge-id: 0x8000.CC:2D:E0:AF:1D:A6
root-path-cost: 0
root-port: none
The election of root bridge happened this way, because 0x8000.CC:2D:E0:AF:1
D:A6 < 0x8000.CC:2D:E0:AF:1
E:63
Now, I have changed the mikrotik1 bridge to lower priority and look what happened. It got promoted to be a root bridge!
[admin@mikrotik1] > /interface bridge monitor bridge-local once
state: enabled
current-mac-address: CC:2D:E0:AF:1E:63
root-bridge: yes
root-bridge-id: 0x4000.CC:2D:E0:AF:1E:63
root-path-cost: 0
root-port: none
And obviously mikrotik2 is not a root bridge anymore:
[admin@mikrotik2] > /interface bridge monitor bridge-local once
state: enabled
current-mac-address: CC:2D:E0:AF:1D:A6
root-bridge: no
root-bridge-id: 0x4000.CC:2D:E0:AF:1E:63
root-path-cost: 10
root-port: ether1-uplink
thats because 0x
8000.CC:2D:E0:AF:1D:A6 > 0x
4000.CC:2D:E0:AF:1E:63
see?
no magic. Plain and simple number comparison. Just ignore MAC addresses because that is like a last-effort solution. bridge priority is the way to go.
and by the way - as long as you don't have any loops in your topology, this has absolutely no meaning because it does not affect anything. (R)STP becomes useful only when loops are created (either accidentally or intentionally)