I just did this last Fall for the following reasons (listed in preferential order):
1. Yamaha/Mercury 90 - All highest quality, + modern , up to the minute technology, large alternator output , strong dealer networks. (Merc is a Yamaha powerhead with their own lower unit). Rather have the lower unit designed specifically for the powerhead.
2. Suzuki/Johnson 90 - Similar to Y-90, very hard choice between these two. Heavier, larger displacement, larger alternator output, but thin dealer network. Not an issue if you have a strong local dealer you trust. Possibly the strongest of the 90's due to displacement, but 40 extra pounds. (Johnson is a white Suzi, so their network is not an issue.)
3. Evinrude E-Tech 90- "The Sleeper"- light, efficient, cutting edge technology, but unproven....perhaps not an issue if you buy a new boat every year and your son is the local dealer, though!
4. Honda- Great classic choice and a proven winner. But rapidly getting outdated and perhaps a bit overrated compared with other newer choices. Still has carburetors and the harder starting. Lowest alternator output of the bunch. 2005 Honda Civic autos still have same three valve/stratified charge head and carburetors, so outlook for EFI not good for forseeable future. How will they meet increasingly tight emission standards? Great track record, but basically same motor sold two decades ago!
5. Nissan, Tohatsu, etc. Too uncommon and unknown to be considered at this time.
6. Scott Atwater, Sea King, Wizard, Faegol, Homelite, Bearcat, Clinton, and other unmentionables with sordid pasts:
If you have one of these classics and it's still in excellent condition, sell it on ebay and you'll probably get enough money to buy a new 2005 motor of your choice! (Force outboards not included.)