Hey Jerry - first of all, welcome aboard!
I can't speak to comparison shopping between the 338 and 358 as I was originally targeting the Sea Ray 340DA when the V358 won me over. It was actually the same situation for a lot of 358 owners here - more details on those reasons can be found on the
V358 thread. But I have some thoughts...
I am a firm believer in the adage, 'buy the biggest boat you feel comfortable budgeting for, for your perceived use.' I also believe that when you jump at least ten feet from where you're at (what are you in now?) you
really feel the difference and, of course, you really feel it in the increase in beam and weight. But it's certainly not essential to enjoying the boat - it just may make you feel comfortable staying with it longer. I had an idea of what I wanted to spend but built in some flexibility. Over my first season with the 358 this boat made me fall in love with cruising and staying on board that much more. As is the sickness, I already would love to have added storage space and even better accommodations for guests, but I'll be moving into a whole other class/size range for that when the time comes. Until then, I'm thrilled with my decision. You're looking at three boats that are, as has been said, essentially the same in design and layout. If you plan to spend lots of time of board, perhaps with overnight guests, I refer you to the adage at the beginning of this paragraph. They're all great choices but more space is more space. And because Four Winns features as standard so many things that are options on competing brands in this class, you are already ahead of the game with Four Winns and the 'bang for the buck' factor.
One consideration is whether or not you want inboards. If you do, then the 358 is your only choice. The other boats will definitely give you more in terms of speed performance. I also recommend you take a careful look at some basic feature differences (as I'm sure you have been). I love having the extra room in the head and the separate shower. There are other things that I believe are only standard on the 358 like central vacuum, which certainly is no reason to choose one boat over another, but enough things on your 'want list' may add up.
Finally - and I don't know if you are thinking of this - in my opinion, the difference in operating costs should not be a major factor in a decision between these three boats. if you really do the math, the by-the-foot differences, while they may add up, are relatively negligible to the big financial picture of ownership. And if you have inboards, some of those costs are negated by the reduced maintenance over outdrives.
As the cliche goes, choosing a boat will always involve a series of compromises. What a happy problem to have. If you have any specific questions, please fire away. If you haven't noticed, we love talking about our boats!