Well, here's some info for you. I just sold my '98 roulette green Speed Triple to buy one of the last S4's available. Here's my take...
I miss my Speed Triple, but I love the Duc too. Coincidentally, the S4 I bought is blue with a white stripe. Custom-painted at a cost of over $2800 so you can imagine how upset I am over the new colors on the S4R. Interstingly, Carlo Di Beagio and other Ducati execs visited Seattle after the WSB races at Laguna Seca last Sumer and saw both my S4 and David Roosevelt's (Owner of Duc-Seattle) custom-built 996 which he converted into a monster. Coincidence? I don't think so and I've written to Ducati to find out if those two bikes were the inspiration for the new S4R. They may never admit it, but it's simply too coincidental for me to think otherwise
Okay, enough of that. Let me say I found the Speed Triple a fabulous bike. I loved it and would buy another. Being a '98 T509 with the 885 engine however, it was not without its quirks, especially the fuel injection, which never got completely sorted out, but was okay in the end after 4K miles.
The S4, by comparision is a fearsome motorcycle and requires some patience and skill to learn how to ride it properly. I kind of like that. Like an early Porsche 911 or a Ferrari 308. Both of which I have lots of experience with... Enjoy the experience.
As for style and looks, well, my Triple got plenty of that, but not nearly as many gawkers as the Monster. It's a trade-off and, frankly, neither of them hold a candle to the Japanese bikes, provided you think of motorcycles as an appliance or as a commuting vehicle.
If you are into stylin' and want to stand out in a crowd, either the Speed Triple - except in pink - or the S4 Duc will do very nicely, but after two weeks on the S4, I'm already leaning toward the Duc as the better of the two, but it's not without some compromises.
I guess, it really boils down to trying to understand if you want to be seen on a bike you can actually afford (I can't) so you'll just have to go see which one suits you best.
They are both extraordinary motorcycles so if you are just one of those people who get upset at, say, Road & Track Magazine, for testing cars you can never hope to buy, don't worry about it.
There are no bad motorcycles. Just buy the best bike you can afford and love it and leave it at that...