General answer: I'd choose the Dell as the build quality has felt better to me than the Toshiba, having owned both for several years both at home and work. The larger screen will be great if you ever want to watch movies or play games. They both have both 15-pin analog and HDMI (digital) video connectors, which is good. Also, the Dell has a Blu Ray drive optionally, while the Toshiba appears to not have that as an option. Make sure you choose the option that has 4GB or more of memory to make Vista happy, and all laptops seem to ship with Vista Home Premium 64-bit, which is a good choice due to the memory maximum being 16GB.
If you're going to be carrying this around a lot, you may notice the extra weight in the Dell, but if you're using this as a desktop replacement, you'll appreciate the increased feature set and options of the Dell.
Here are some things I noticed:
Slightly lighter in general.
I've never really liked this style of hinge (inside, cantilever), as it feels like it's more likely to break due to the design and levering motion. Also, if you have something directly behind this laptop, it may make it challenging to open this unit. You will need to use the system-memory sharing Intel Graphics Media Accelerator. I personally prefer to have my graphics memory as close to the GPU as possible, and not being shared with system memory.
Screen is two inches smaller.
No Bluetooth card option.
Dell Studio 15:
Brand name is slightly more trusted build/quality wise than Toshiba on the laptop end. The screen is over two inches larger diagonally. The hinge is on the outside, so seems like it would have fewer problems and not attract dirt/dust as much as the Toshiba hinge. The keyboard is really nice, plenty of room to type, and has a pleasant key throw.
Although the lower-end of this laptop comes with the Intel® Graphics Media Accelerator, there appears to be the option to have a 256MB ATI Mobility Radeon HD 4570 installed, which would be a preferable option. Toshiba does not appear to have this as an option.
This unit has a Bluetooth card option, which is useful for having Bluetooth headsets and mice.
Slightly heavier, but you have a really nice sized screen - over two inches diagonally.