I wouldn't look past an opti 75 or 90. Big engine but great on fuel and all the power in the world. I feel hydrolic steering is a must if you are going to bolt a large carbed 4s or opti on, or the craft will be twitchy at wot.
Having said that, if you can find a nice second hand honda 75/90 they are a great engine on a searider.
I've been through a yamaha 75 pro 2s, yamaha 80 2s, yammie 90 2s, they all give like for like performance with a 17P SS prop.
I've also had carbed 4s merc and mariner 75's, a wee bit heavy but good on the juice. Watch out for big end bearing going on them. (There is a nice cheap one on fleebay for £2250 item number - 261629467158)
I've had a twatsoo 90 2s that was good lump but thirsty like the yammies.
I've had a Suzuki 90 4s efi. Good engine but seriously heavy!! About 185kg. Not as good as the opti on fuel.
The opti is a nice unit but can be expensive to service or repair and is full of electrics.
Never had an etec