i agree with armistice; with a separate interface you can easily change the mic for something else whereas with an "all-in-one" usb mic, if you don't like it, you are then in the same boat of either replacing it for another usb mic
or getting an interface and mic.
within a $300 budget for both mic and interface there are a lot of options that all kinda depend on what you need from both. are you planning on just recording vocals or do you want to record more stuff as well i.e acoustic/electric guitar, drums, bass, etc etc?
With all mic purchases you're best off trying as many mics as you can, especially if it's for your voice. All the mic's you've mentioned have their pro's and con's and may or may not work on your particular voice. I appreciate, as it comes up alot, that it's not always possible to try all/any of the mics you're looking at so the other options are; try and find someone with the mic/s that'll let you try them, talk to local studios and see if they're let you try some, and if worst comes to worse there are plenty of audio examples all over the internet (although they do all need to be taken with a pinch of salt). if you've got any links to examples of your voice then post them up as it's sometimes useful for people to have a listen to help recommend mic's.
in terms of interfaces, the fast track isn't awful and will certainly do the job it's designed for. however, as i said, if you want to record more than one track at a time then it may be worth looking at some other interfaces. i know they cost more than
the fast track (which at $50 is hard to beat price wise) but things like
the Presonus audiobox,
focusrite scarlett 2i2 and Saffire 6, and Tascam US-200 are all great little units. if you've not read the sticky about choosing audio interfaces i recommend having a good read as there's some great advice in it.
