Most honest answer: all depends on the personality/style of the caster and campaign.
Elaborating more:
If you are a "good guy" type of person you could go with soft and extremely effective spells like
Sleep, paralize or Force bands.
Pros: Extremely effective, and hard to resist. One shot - one opponent out of combat spells. And can also be used to effectively prevent combat.
Contras: Lots of prisioners after combat situations. In some campaigns that can be anoying or way too cruel tio execute everyone everytime. Some opponents could be immune or at least resistant to then (never saw a skelleton taking a nap
).
For a more scary build the
damagin attack spells or
paifull ones can do the trick.
Pro: More consistent with most combat situations and campaigns. Most DMs wound not have any trouble with these spells.
Contra: less effective tacticaly.
Jolts deserves mentioning too.
Pro: Stuns and uncosncuiusness effectively disable opponents and is consistent with most climatic battles.
Contras: same as sleep-like spells, you will need to finish helpless opponents most of the time, but at least they are not pacefully sleeping.
I can think of many possibilities but they are realy campaign dependant. Can you tell us more about the character and/or campaign?
PS: about elemental spells: they do seem inferior on the first glance and they indeed are if your DM uses just straightforward combat situations, but remmember that elemental spalls can be used in the same way warrior uses their weapons: to destroy objects, to cut ropes, to bring down doors etc.