i have kept cons and firemouths in the past, and currently have a full grown male GT in another tank. All i am hoping for is a few large relatively aggressive cichlids that will be ok in the 150. Tell me your opinion on each individual fish and what they are like if you have kept them:
cuban
vieja fenestratus
red devil/midas
jag
dovii (couldn't help myself, love them! how long would they live in a tank this size?)
trimac
Skip the dovii (odds are you'll get attached and not want to get rid of them), if you like the body shape and colors go for a Grammodes (mini dovii), Trimac would be my other choice.
you could keep a dovii in that tank for a couple years or until it reaches 14-15" however this fish will need to be ALONE with no tankmates after it reaches 5" or so. if i were you id do a dovii then upgrade to a 240+ in a couple years