If you really want to see a lot of info on these two grills, check out the Barbecue Source at
http://www.bbqsource-forums.com/invboard/index.php . The Source is my "other" grilling/smoking forum and you'll find lots of great and well-informed information. Use "Search" on "Genesis 330" and on "Summit 420". (Recognize that the 420 is just the lowest model of the Summit line -- it's a question of features between the different Summit models -- and PRICE, of course.)
At the Source you'll find more than you can read on N/S vs. E/W., New vs. old Genesis, Genesis vs. Summit and use of rotissieries on any. (I would disagree that the N/S burner orientation is "worse" than E/W -- it's mainly a question of learning to use either properly.)
For my part, the Summit is a little more expensive, PROBABLY has more quality SS internals (good luck getting Weber to give any details on that subject), will get hotter (say about 100* more?), has heavier construction, and comes basically assembled where the Genesis requires a couple of hours of your work (unless you buy at Ace). Either are superbly designed, will last at least 10 - 20 years and have great long and well-supported warranties.
My older E/W Genny has converted me to a dedicated griller who has really no fears of trying something new -- anything. Before the Weber, I tried to produce edible food on a grill that cost just as much but was a POS. With the Weber, I can focus on cooking -- sweet!
If I had the choice with what I've learned, I personally would buy the new SS Genesis 330 over the older E/W (other than the E/W burners which I love, the new Genny is just better designed). I would take a higher end (470 or 6xx) Summit over the Genesis 330. At the 420 vs. 330, there is a small plus with the 420 -- it's up to you whether it's worth the cost difference.
Rich