My votes:
Finger of Death, Mage's Magnificent Mansion, and Summon Monster VII
Why?
Finger of Death is a very good spell for removing living enemies from the field. There's usually a moderate chance that it'll remove them completely, and if it doesn't, it still does a reasonable amount of damage--especially at level 16+ (3d6+16=average of 27). It's not as good as Destruction but it's pretty close.
Mage's Magnificent Mansion is the ultimate in home security. It can't be scried, can't be teleported, and can't be entered without your permission. As a 16th level mage, you undoubtedly have powerful enemies. This spell limits their options when attacking you. That's easily worth a 7th level spell slot for a 16th level wizard.
Summon Monster VII is a very good and flexible spell. For battlefield damage, a celestial elephant trampling will inflict more damage than anything except a firestorm--and more than a firestorm if it survives for more than a few rounds. Elementals are good meat shields Djinni, Avoral, bone devils, and babau all have a lot of uses and even its multiple lower level options (1d3 celestial polar bears or Bralani Eladrin, giant constrictor snakes, or celestial dire lions, or 1d4+1 hound archons, celestial brown bears, bearded devils, etc. are very useful options.
As for the competitors:
Limited Wish is very useful but the 250xp cost makes it hard to justify having it prepped every day. It's very good but not something you want to cast on a daily basis.
Forcecage is even more expensive. Useful but too much of a corner case to keep prepped all the time.
Prismatic Spray has some potential good effects but is too random for my liking. Sure, it could turn your foes to stone or send them to hell but it could also do 20 points of fire damage, save for half. Not so impressive.
Spell Turning has too short a duration to be useful when you're not expecting trouble. It's handy if you are, there are quite a few other nice buffs you could use. Ones with more general utility.
Reverse Gravity seems a bit too dependent upon the situation. Flying foes are more common at 16th level than undead/constructs. Good spell, but I don't know as I'd prep it every day.