First: for an XLR mic you will need an audio interface (just a big soundcard) with 48V Phantom Power AND and XLR input. Another 100$ - but this will give you a good external soundcard that is made for stereo (no surround etc) output and some inputs. Dont expect better sound quality - but an external soundcard has other advantages (volume control on your desk, input/output on your desk too and more power for your headphones). A mic preamp (usually tube) is also an option (combined with a soundcard or just standalone for your onboard audio).
USB is simple - plug&play. Not much to say about it - it works. Dont plug it into a passive USB hub, make sure its on USB2.0 (there are no USB3.0 mics and some can make problems on USB3.0). But USB is also a big "problem" if you want to use your mic somewhere else.
Most people are using USB, Pistol is using the Blue Yeti (USB).
http://www.thomann.de/gb/blue_yeti.htm
There is a Pro version too, but its pretty expensive. This thing is huge, heavy and pretty popular, its working great (just check her twitch channel to hear how it sounds like and compare this to a youtube video on tek syndicate with her voice etc).
I have an external XLR mic (Rode NT-1A and some other), the ART Tube MP preamp and Terrasoniq Phase x64 USB audio interface with like 20m on cables, it has an external power supply etc. More cables, expensive - but i can do more (as a DJ i need some flexible setup that i can connect to anything).
Try to get a Samson Meteor Mic (great quality, pretty cheap but still sound amazing and its looking good, the oldschool shiny metal design - sexy^^) or the Blue Yeti (big, heavy, expensive - but its vesatile and sounds a bit better, you can actually record instruments and vocals with it and get decent quality).
Additional stuff like a mic stand, popkiller (not needed but you may want one if you are close to your mic) etc. - you can buy it anytime, each condenser mic will work with a mic stand.
XLR is worth it if you have a camera/mixer etc. There are more condenser microphones out there, but i`m living in Germany and the market here is a bit different. But you can grab a great mic for like 200$ or less.