I own I1Pro 2, I1Profiler, an Isis XL 2, PM5, and ColorThink Pro. I also have Argyll installed in a VM and Matlab "Home" in my main machine.
I agree with the points made by others in this thread.
I've found I rarely use ColorThink Pro anymore. For analysis and exploring questions of profile quality I almost entirely use Matlab and the image toolbox.
I generally make profiles and other test charts with I1Profiler though Argyll is very good. I would use Argyll primarily and only use I1Profiler to get CGATs files except that I1Profiler has slightly better performance on 9800 neutrals. But they are quite close. I1Profiler's perceptual table is fairly useable too. Argyll requires some work to create Perceptual tables that are different from RelCol. By default, Perceptual is the same as RelCol. However, you can customize Perc. and will have a lot more flexibility with Argyll if you want to experiment with different Perceptual table mapping.
I also use only Argyll for profiling my scanner. It's easy to add a lot more patches with a printer chart and make much better profiles for scanning prints. It's just as good as I1Profiler for standard IT8 charts.
ColorThink Pro does make some pretty 3D plots though and they are quite good looking. For large data sets, and fast calculations Matlab runs rings around it. OTOH, you have to be comfortable with scripting to get much out of Matlab while ColorThink Pro provides s more intuitive GUI. Argyll is powerful and there are a lot of utility programs that generate cool things, plots, conversions to txt to load into Excel and such. If you intend to go deep into understanding color management I'd start with Argyll. You can go back and forth with I1Profiler since they can both read CGATs files. You can make charts with one and process them with the other.