When considering voltage divider, you have to consider load as well.
If your microcontroller or amplifer that requires voltage from such voltage divider you have to consider this:
What is maximum ammount or error in application in question?
Is there a low power consumtion requirement?
Is high frequency involved and how high?
What is load current draw/ input impedance?
Does load have spikes in current draw ?
Does power supply has interference or noise that needs to be supressed?
What is bandwidth of signal needed?
What is the temperature range of this circuit?
.... and probably many more that I forgot...
If you address all of these questions you could write a book about just a simple voltage divider, as LvW already pointed out infinity of possible solutions. So to limit our questions, let's assume that is voltage divider is to work only on dc and without temperature consideration.
If that is the case than only thing you have to consider is power consumption and voltage change under load current draw. These two requirements are completely opposite. For low voltage change you need to reduce resistor values as low as possible, and for power consumption is opposite. Obviously, you have to make compromises. In your case if we have ±1µA of load current draw with 1k version voltage variation will be only ±1mV, but current draw from power supply will be 2.5mA. Version with 100k will draw from power supply 100 times less current, but will have error 100 times bigger.
±0.1V for 100k case would represent ±4% error on 2.5V and in some applications that might be good enough. Low consumption of power might makes this choise much better in such applications. Well, this was simple?
Unfortunatelly this is just the begining of error calculations. After this comes bandwidth of circuit, noise, Tc effects, ...
Read OpAmps for Everyone, free book available from Texas Instruments web site, it will help you in understanding sources of error in analog circuits.