Obviously, anyone will choose their current software as the best. Especially if they've been using it a while and are familiar with it.
To them it will be the best in class. Another designer may or may not agree, they will have their own familiar package which would be better.
Assuming the choice of software is required for future career progress, then you should look at the industries that you are interested in and then look at their software choices.
As a rule, the larger the industry or company, the more high end software they will choose. This is either because they believe it will do their job better, or the appropriate marketing team have persuaded them. Often they will follow the development path to minimise the impact on legacy data.
Hence this is why AutoCAD users migrate to Inventor. SolidWorks (as you will be aware) has tried (and is still trying) to lure AutoCAD users to SW with their read and write capability of ACAD files; however the upward migration to CATIA isn't so clear, but then again, you may never need CATIA anyway! Similarly SolidEdge users migrate upwards to NX, however this is smoother than the SW to CATIA path. My impression is that the PROE/Creo environment has a loyal following, but fewer new take-ups - it could have a niche for esoteric reasons, but it wouldn't normally be something to focus on for a career boost.
The smaller (by user count) packages like SpaceClaim etc. could be limiting to you, due to the reduced demand for the expertise (currently). So, while they may be accessible, you may find you won't get much exposure to the skills you gain from it.
At the SW level, then the main competitors are Inventor and SolidEdge, and at this mid-range, the training can prove to be difficult to do cheaply, since their focus is on getting companies to train people and/or convert to them. CATIA and NX are a cost level higher and probably even harder for an individual. ACAD is not a direction to go in, as AutoDesk are preferring Inventor over it.
Finally, you have to get access to the software, and we are all aware of the costs here, and you don't really want to be spending the money on software you'll never use again.
Once again, look at the industries and companies you're interested in and learn whatever software they're using - at the end of the day, it's the interface you're learning must of the time, the techniques embedded in the ACIS/Parasolid kernels are fundamentally the same.
