Pete - Its all in what you need, what you can afford (now and on gas) and what type of water you fish.
I bought a used 700lx DC last August (From the guy who runs this site) it's got the 115 carb'd merc on the back and I love it. Its just 17ft even, has a lot of storage, rides great in moderate chop, and will run into the low-mid 50's.
If I was tournament fishing i'd definetly want an 18-19fter with the Max HP, but I am a weekend angler. The Livewell on the 700 is 28 gallons (divider so you can pull it out if you need more space for # or size of fish). The space behind the console is a bit tight, so if you are large in the gut it will probably not fit you well, though there is WAY more then enough leg room under both consoles for a 7fter!!! LOL
Trep