I love the choice of Open, Group and Solo. I plan to dip into each one whenever I feel like it. I love player choice, after all - who wouldn't?
I first played in open mode more or less up to obtaining enough money to fully own and outfit an Asp. However, I'm now more inclined to use solo mode for pure trading, now I own a Type 7. Since this is a huge investment for me (and purely a trading vessel), I can fully understand the desire to play in solo mode to simply grind for credits, (to allow for the ownership, upgrading and - crucially - RUNNING of higher end vessels.) Ideally, I would like to obtain enough cash to afford a fully kitted out Python, which I've heard is a great multi-purpose ship.
I suppose, the key thing for me is time. I don't have great amounts of time to play this game; so, what time I do have, I'd like to spend mostly moving forward towards my 'credit goal', rather than recovering from needlessly being destroyed by another player. I guess I could do this in open as I am engaging in trading 'off the beaten track' - I still might consider this. (I would tend to avoid the core systems, of course (Lave, etc)...too many player interdictors).
[Incidentally, I know grinding is, by definition, a repetitive task, but I still find it quite relaxing and satisfying ... up to a point, of course!

]
However, I also enjoy dipping my toe in the water of open play with my cobra. It's kitted out nicely but cheap enough to replace several times over. (I am fully aware that my PvP skills are somewhat limited) I mostly bounty hunt or practice general combat in this ship, to add a little variety to proceedings.
My personal goal is to own a higher end multi-purpose ship (the Python), after which I will mostly play in open, or group, mode. For me, my reason for playing this game is to enjoy the simulation and experience, while trying to avoid frustration for as long as possible! I don't seek PvP play, but if it finds me, I would like to reach the stage when I accept victory and defeat in the same way - in that, it's all part of the game, and that the loss of cash isn't such a significant waste of time. Not quite there, yet.
Anyway, choice is good. I realise FD are still balancing the game, as there are obviously aspects which still need work; but the core experience is good enough for everyone to find something which suits them.