Illusion/Traps - so versatile, very different playstyle, a bit better solo than on teams due to the nature of /traps being mostly immobile and longer-ish recharge; but you also build for recharge for illusion, which helps traps though, so when recharge is built up, even on teams some of your traps are always useful and up for the next group or every other group. Plus teleport to move them around. This build excels at moving ahead of the pack, not trailing behind.
Illusion/Rad - versatile, works well doing anything, really - lacks some of the tricks and damage of /Traps but is easier/cheaper to build for recharge, a tad bit more group friendly than traps. Lovely lovely AOE hold toggle in /Rad. Proc it for effectiveness and stacking Hold on bosses. Same as /nature.
Plant/nature - as I said, king of AoE, solid support set, really shines in groups. Very thematic.
Plant/Marine - about as good as nature, maybe a smidge better for damage and buffs, but its really apples and oranges. Theme is strong here. Go Leviathan.
Gravity/Dark - Strong single target damage, best pet ever, combined with a fantastic dark fluffy in /Dark, you get the whole package except a bit light on AOE, but you can proc bomb the stun if you like, add in incarnates, epics and temp powers, you're fine. Super safe. Feels stronk.
Arsenal/TA - kind of like a controllery Rambo build. Lots of damage potential, not enough keys, so make sure you keybind lol. You are the swiss knife/tool kit/boy scout kit. Great for a gadgeteer!
These are the ones I have and are familiar with. I would recommend them to any who want a controller.
Best budget controller: Gravity/Dark.
Best newbie controller: Plant/Nature.