The W-series cameras tend to be the better cameras overall than the T-series cameras for pure image quality and features...they are designed to be more conventional high-spec compacts with traditional pop-out lenses with less elements to have to focus and see through and slightly faster (read: brighter) lenses.
The T-series cameras are designed to be a mix of solid compact camera guts, but with fashion and design thrown in, as well as compactness and portability. When powered down, they're both reasonably small for a pocket or purse, with the T90 being nominally smaller. But when powered up, the W-series lens pops out of the front like most cameras, whereas the T90 stays exactly the same. The lens is what is referred to as 'folded optics', a creative way of reducing the camera size by having the zoom work vertically within the camera body, and using a mirror and glass outer element to seal everything inside the camera.
Deciding which is more important to you - going for the absolute best capability you can squeeze out of the model, or going for the style and design with a slight compromise in overall capability.
The W290 is the better choice for the slightly more sensitive lens (F3.3-5.2 vs. F3.5-10), the wider angle (28mm vs 35mm), and the longer maximum shutter of 2 seconds compared to 1 second.
BTW...I chose the T-series myself in the T100 a few years ago...I wanted a compact camera to be a companion to my DSLR, so I was willing to compromise on overall feature control and image quality over a similarly priced traditional compact because I liked the extra-slim profile and sealed lens, and the cool style of the camera. Since it isn't my main camera, it's OK to have one that's fun and stylish, as I can always use my DSLR when I want to go for maximum image quality. And the camera has served me tremendously well, providing some beautiful shots and even some artistic type shots. Learning how to get the most out of any particular camera is the most important thing.
As for better or worse with different brands...of course it would always behoove you to look around at other brands and never limit yourself to just one brand...you never know if the perfect camera for you is out there but with a different brand name than you expected. But at the same time, don't worry about x brand is better than y brand...for the money, most compacts today are pretty darn near equal, with only minor differences in features, controls, and image quality when comparing similar models and sensor sizes...and none of those differences are likely to be exploited by typical camera buyers. Switching from Canon to Sony to Nikon to Panasonic to Olympus and on and on is not going to give you anywhere near as noticeable a difference in the quality of your photography as learning fundamentals of photography and how to best use the tool you have. And while there are better cameras out there than the two you named...they are generally in different price points or form factors. All manufacturers tend to offer several lines of cameras, ranging from basic cheap models, to stylish models, to solid mid rangers, to top of the line models, to semi pro models with manual controls...and to DSLRs.
Hope all that helps! Huge answer, but to basically summarize, the W290 will likely be a slightly better camera overall for image quality, while the T90 will be slightly more compact and more stylish in design.
