It really depends on the uses.
Let me give you my recommendations:
General desoldering work - T12-D24 (unless working with very tight spaces)
General soldering work - Use T12-D24 and 0.8MM solder
Soldering work where the solder joints are very close together (not much spacing in-between) - Use T12-I and 0.5MM solder
Soldering Plugs to a wire (or soldering SMD resistors/diodes) - T12-I and 0.5MM solder
Using drag soldering technique for various chips/ICs (with reasonable leg spacing) - T12-BC2 or T12-K and 0.8MM solder
Plating wire ends with solder - T12-I or T12-B (this can technically be done with any tip, but I find it easiest to do with conical ones due to the shape)
Hope you found this useful, and good luck!