Round table

Devils are placed in 33% of cases on the 1st... well, who then can stand against Inferno on the 2nd from a rush? ;)

To build bears you need to spend 1k+2.5k+10k=13500 gold and 10 crystals
To crank out devils 1k+2k+3k+4k+15k=25000 gold and 23 mercury.
The difference is 2 times.
And if bears on the 1st are placed quite problematically, then to put devils on the 1st you probably need to have a respawn like on Jebus Cross, where gold is everywhere you spit.
And if it so happens that you've built orcs and ogres through the low current penetrating power of the army and you'll have a choice between putting bears in the fort or building a stronghold and castle, then I'd rather choose the latter option, which will cost 1k+1k+2k+2.5k+2.5k+5k=14000 gold