With my articulation students, I use a couple of things. First, I use the S-CAT.
It's a great way to have something on paper to compare progress from year-to-year. I can look back and see how a student did the previous year, as well as determine what (if any) contexts work to his/her benefit. The downside is that it does take a little time, and the student just repeats words, phrases, then sentences to you. The upside is that you can get a percentage correct from the responses, and, as stated previously, you can see if there are some sound combinations that work better than others for the student.
For baseline data, I use my artic cards. Since I only have 1 set of Webber Artic Cards to use between 2 schools, I use those at 1 school, and my artic cards that I made a loooong time ago for my other school. I take data (either correct or incorrect) on the productions attempted (first attempt only) with all of the cards in that deck (28). And there I have my baseline data.
I progress monitor my artic students through therapy data. At the end of the session, I put a dot on a chart to indicate their accuracy for that session and they draw a line to connect the dots, but only if we went through all 28 cards. If we didn't get to all of them, they don't complete the chart. (I think it came from Year 'Round Lifesavers and Timesavers for SLPs from Super Duper, but it would appear that it's no longer in print.)
Honestly, I don't think it matters what you use for your baseline data & progress monitoring, as long as you're consistent. If you're not consistent, you're not getting a good representation of progress.
HUMONGOUS shout-out to Sparklle SLP, Speech2U, Talkin' With Twang, and Speech Sprouts for getting this linky together and for doing all the work!