Staging options

One stage, single rocket engine. Least complex, but least efficient in terms of amount of load it can carry. Waste of extra fuel. (special case of serial staging design below, when n=1).
Serial staging with a single rocket engine per stage. Consider 1 or 2 or 3 stages stacked on top of each others. More efficient, but does not provide as much thrust as parallel staging or clustered engines.
Clustered design. More than one engine fired at the same time. Can be used in single or multiple stages. Adds more thrust. But clustering is usually done at lower stages (left off stage) where the extra thrust is needed. 2,3 or 4 engines are typically clustered together.
Parallel staging. Shuttle is best example. Extra solid fuel rocket boosters added to the sides of an existing rocket to increase left-off thrust. Discarded shortly after left off. Parallel staging is used for lower staging only (earth to LEO). For upper staging (LEO to GEO) it is not consider needed due to lower thrust requirements Hence will not be considered here for the LEO to GEO design.

One stage, single rocket engine. Least complex, but least efficient in terms of amount of load it can carry. Waste of extra fuel. (special case of serial staging design below, when n=1).