If you can create essentially the same illustration in any application, how do you choose one over another?

Vector or bitmap is a critical decision for any illustration as you consider how the work may be used in the future. Although tools have blurred the key differentiators recently, there are still major differences to the tools like Illustrator or Photoshop.

A vector-based application using mathematical calculations to determine, say the arc of your line-work where a bitmap program uses actual pixels based on where and how long your line may be. If you are planning on using the work for a single intended purpose, this is usually not a concern.

However, if you plan on scaling the work up for magazines, t-shirts, billboards, etc. a vector program provides greater flexibility for using your artwork across these outputs. Scaling a mathematical line will render that line perfectly, regardless of size but scaling a bitmap line will introduce noise to the work and make it appear blurry or dirty. 

Vector programs are also used quite a bit for typography and publishing projects. Although bitmap applications can certainly handle fonts, Illustrator offers a lot more control of letterforms for page layout and font creation.

Plugins extend the functionality of specific software that enhances its capabilities and helps an artist to remain efficient and effective when producing artwork. 

You can find plugins for virtually any industry that streamline the handoff from artist to production staff. I use a set of plugins for much of my work from the great team at Astute Graphics. These plugins range from texture creation to file health and have proven quite indispensible for my workflow.