I was pretty much half-and-half between solo and team play. When I just wanted to self out, I'd type /hideall and often that meant I would be spending the evening on one of my tanks, or maybe a higher level blaster or controller, just enjoying the stories and some "head canon". (Side tangent--a couple of friends who knew me well enough would send me /tells during my normal play-times even when I was hidden--I never thought I would miss that; boy was I wrong). I was just warming up to scrappers when the game closed, which was hilarious because it made me realize how much time I'd spent making a couple of my tanks "scrappy".
But when I was feeling social? I LOVED defenders. I used my tanks on teams as well, but unlike their versatility, I had long since given up soloing with defenders. I often heard rumors of solo-capable (and FUN to solo) defender set combos. I never personally discovered one of those combos. But on all of my defenders, at least one thing was for sure: whether in the light or from the shadows, I was contributing...I was sometimes contributing in a big way (depending on the powers and slots)...and my contributions always felt worthwhile.
Eventually I learned how to solo blasters at lower levels. This was no small feat, being a tanker at heart. Low-level controllers on the other hand--for my purposes--those were just another kind of defender. In teams they made REALLY effective defensive comrades, even at lower levels. Controlling the battlefield like it was a game of Chess, a game of Chess in which you could cheat the rules by all sorts of advantages for your team and disadvantages for the bad guys. Around level 30 or so, things always seemed to open up for my controllers and I would suddenly have access to one or two game-changing powers that allowed them to take the world by storm, with or without a team.
Of course, these are the ruminations of a "casual" player. I have to use the air quotes there because I played an awful lot. But unlike the hardcore types, I only ever cared about the journey, and my gut was my build-planner. A lot of people were surprised to hear that, especially those who fought alongside Captain-Electric or my tank the Sapien Spider. I think the reason my builds turned out well was because I fine-tuned them along the way, always looking ahead at the larger picture, and the way was long, leveling slowly or often XP-less through story content, and becoming familiar with each and every level to 50. Of course I don't think I had anything special on the min-maxers, but I could keep up with them and that's pretty cool. Anyone who played the way I did no doubt knows what I'm talking about. Over time you developed a feel for things, and you learned to trust your gut.