It depends what you're using them for.
For general electronics work, you might be able to get away with 1/4W for everything.
These days 1/2W are about the size that 1/4W used to be.
If you need the dissipation, then you need to get a resistor that will handle the appropriate amount of power. Typpically you want something that can handle 50% to 100% more power (at least) than you are dissipating. This will prevent things getting too hot. But using a 50W resistor in place of a 1/8W resistor will generally do no more harm than take up more space and cost a lot more.
Another thing is the voltage rating for capacitors. This is rarely anissue, but where it is an issue you need to be aware that higher powered resistors often have a higher voltage rating and that placing resistors in series allows you to add up their voltage ratings (as long as the resistance values are equal). Voltage ratings are often in the region of 200V, so for electronics powered by batteries you will typically never have to worry about it.
If size is not a concern 1/2W metal film resistors would be fine for most low power stuff. If you ever need a slightly larger dissipation you can place resistors in series or parallel.
