That depends on several factors
If you are designing something that would go to some volume in quantity, then it would need to be manufactured by an EMS with pick and place machine, reflow oven etc in order to decrease the production cost. Even if you are on prototyping stage, you should use the cheapest and smallest components as long as they satisfy the requirements. In general smaller components are cheaper, but there are exception like high capacitance or inductance in smaller packages might be more expensive than the larger packages. In general you would like to chose smaller components to be able to decrease the size of your board.
If you are planning to do hobby work, course project, or so, then it depends on your experience and tools.
If you have good tools, then soldering 0402 is easy, but if you don't have any experience and bad tools, 0603 or 0805 (and higher) would be easy to handle. You should avoid to use QFN package, it is requires long to place and correctly solder. In addition, try to chose IC's that has larger pitch size.