i also play solo singer/songwriter/acousticy stuff and use both types of guitars in different tunings, for what its worth. I'd go for the ibanez if i had to have humbuckers or wanted that giant body sound. i'd probably consider some pickup/bridge/electronics swaps further down the line, but i do that for any guitar anyway.
it seems to sound exactly the way you'd think- like a casino, but smaller/less. Judging by this video, it seems the casino coupe has just enough prettyness and hollowness to imply 'casino', but in a more manageable size with a little more solid/semi qualities to give it some extra versatility (at the expense of the bigger, airy, hollow sound). the p90s can be warm or they can jangle, the middle position is hum cancelling and they handle gain fairly well, better than the ibanez would. it'll feedback a little less but still impart a hollow sound, though not to the extent of the ibanez. Given the two options, i'd pick the casino, based on my experiences. i'm guessing the ibanez is a es175-ish kind of thing? if so, the current epiphone es 175 premium with the lacquer finish and gibson pickups might be something to think about, if you're ok with the jump in price. Like you, i haven't played either, but i own similar guitars, including a gretsch and an elitist casino.
