In general, you want the largest display that you can afford if you go with a fishfinder GPS combo unit. However, the size of the instrument hatch on the 226 limits the height of the head unit that you can use.
IMO, the best bang for the buck for a unit that will fit is the Humminbird 958. This has an 8" wide display that fits nicely in the compartment and is easy to read when you split the screen to display both bottom and navigation information.
This is not a side imaging unit, so it costs a lot less than the more popular 998. So you can find great deals for them on the web. I've seen them for sale new for around $600.
I have a 997 in my 226, so I know how well the unit will fit and how easy it is to view. I find that I hardly ever use the side imaging function in saltwater, so you are not giving up very much to get a unit for half the price.
