250-300 would be good, even 2 each 150s, but you would need to watch for weight if they are 4 strokes. Are you thinking new or used? If new, I would be tempted to go with one of the new Mercury 4.6L V8s, in 250 or 300 (same engine). Used? A recent 250-300 Optimax (2 stroke!), Pro XS, or V-Rod, followed by a Suzuki 250-300 at 600-700+ lbs, the Zukis are heavy!
You can probably get a deal on an ETec these days, since they have announced they are closing down - parts will likely be available for 10 years - but you never know...
And twins? You can still buy new, last year model Merc 115s - the Merc 115 ProXS 4 stroke is selling for about $9,000 new - a pair for 18,000 new. New 250s are going for about $25,000 - never made sense to me, but you can buy two 150s for less that one 300. A pair of 115 to 150 would be sweet on that boat - and if you are going offshore - the safety factor for two engines is a consideration. You can also look around at a pair of 4-cylinder 125s that would be OK weight-wise as an option.
So many choices! Good luck!
