Indeed, there are some very decent plugins for Avisynth. On the other hand, there are a lot of plugins that are nothing really special and any NLE will be able to do similar/equivalent work. Still, there have been times where I continue to use Avisynth myself due to the superior results when it comes to removing certain types of artifacts, especially "rolling rainbow halos" on VHS footage (something I'm dealing with again, on a job right now) HOWEVER, there is a rather steep learning curve when you start tweaking settings and/or when you are using multiple plugins in a chain for the same piece of footage. What makes the curve so steep is the lack of a "centralized package" where all possible plugins and all documentation can be found. It's scattered all over the net and sometimes you have to "hunt" info/plugins down. The upside is, that there is a TON of this stuff to be found and you can get lost for days once you start reading it all; it's happened to me, LOL
Pretty much just like with anything, a lot is determined by user skills, needs and "style of work" (aka - workflow) which is true of NLEs too... As far as ease of workflow, speed (of real-time changes in preview and rendering) and MY personal experience, I use Sony Vegas Pro 11 for most of my video work in the
editing stage. (deinterlacing, IVTC'ing, etc., doesn't fall in that category and that stuff I never do with Vegas due to inferior results) This doesn't mean that I think it's the best app, as I know there are things it can't do that are standard on the other common "big boys." I think there is too much clutter with some of the other apps and while I appreciate all of the extra options, it's just too much for me and I don't like the way the workflow is on the GUI for my projects. However, I've had to look past that when I have needed something specific done that Vegas couldn't do and I couldn't figure out using Avisynth scripts.
The thing that bothered me mostly about using the scripts is that I would have to wait until the file is rendered with a particular set of settings before I could see the results and this presented the biggest challenge for me when settings had to be customized, particularly if using numerous plugins. As a "work-around" I use the "avsproxy" inside of Avidemux 2.5.6 that gives me a preview of the results BEFORE rendering. The only downfall to this method is that the preview is not in real-time and you have to make the changes and then restart proxy and then it updates preview display in Avidemux. Still, this is a LOT faster than rendering sample after sample after sample JUST to see the changes. To the best of my knowledge, this is the only way I have been able to find where there's a preview prior to render using Avisynth scripts. If anyone here can enlighten me to a real-time preview, (as I have in Vegas on a frame by frame basis if necessary) when using scripts - feel free to post here
If you need any help setting up the avsproxy and avidemux or any tips - feel free to ask as I have been using this method for about three years now and might be able to help you avoid some of the annoyances when learning this crap
But this doesn't mean I am a master of avisynth, just not a noob