From a wildlife perspective the Falklands, South Georgia and Peninsula itinerary is certainly an amazing cruise. It depends on when in the season you go but the main differences between this itinerary and a Peninsula only cruise are that you will see courting/nesting Albatrosses and Macaroni and King Penguins which you will not see on the Peninsula cruise.
South Georgia alone is a really amazing location with huge concentrations of wildlife and it worth a visit by itself but if time/money is a restriction you certainly will not be disappointed with an Antarctic Peninsula cruise.
Another note is that on a Falklands, South Georgia, Peninsula cruise you do not spend as much time at the peninsula. Compare itineraries to see differences.
There are some really incredibly beautiful locations further south on the Peninsula that you may not reach on the Falklands, South Georgia, Peninsula itinerary.
If sea sickness is an issue then time in open sea is a lot less on a Peninsula cruise too. You will spend 4 days total crossing the Drake Passage (2 days each way). Once you reach the Peninsula this ship is sheltered from open seas.
A note on sea sickness. Crossing the Drake Passage can be calm, rocky or rough depending on the sea conditions obviously. There are precautions you can take to minimise the effects of sickness but if you can put up with the discomfort it will certainly be rewarded when you get there.
Having said that you may not have any problems at all. I have travelled with groups in rough conditions and they have not had much problems providing they took precautions.
I personally use ginger (in the form of drinks) to help alleviate sickness and have given it to others with problems and it has helped them. There are also other drug based options including patches and tablets or wrist bands which work on pressure points. It really depends on your own preferences.
Hope this is of help to anyone thinking about a trip to the great white continent.