I sing to my birds all the time. It's not a pretty sight, or sound, that's for sure, but the birds seem to enjoy it. My family is always telling me I should sing tenor.....ten or 12 miles away from them, hehehe. Glad the birds aren't so critical. The more I belt it out and the more off key I am, they start yelling and singing along. I also leave the radio on for them when I'm out of the house.
Concerning your decision, omg, how does one decide? Besides getting them both, maybe you should meet a couple from each species and let the bird pick you. I'm a big amazon lover so I don't think you could go wrong with any of them. Good luck!