Each has multiple nuances. I will write typical meanings and example sentences that are often used.
すっぱり
- Cutting things sharply.
えだをすっぱり切り落とした。
I hacked off a branch.
- The act of doing something decisively.
旅行の計画をすっぱりとあきらめた。
I gave up the travel plan. (just like that).
すっぽり
- How things fit in and out.
子供がすっぽり入るくらいの大きさです。
It's big enough to completely fit a child inside.
- The state of covering the whole.
街全体が雪ですっぽりとおおわれた。
The whole city was completely covered with snow.
さっぱり
- Discomfort and feeling of discontent are completely gone and you feel good about the situation.
友達と仲直りして、さっぱりした気持ちになった。
I made up with my friend and felt refreshed.
シャワーしてさっぱりした!
I took shower and (now) I feel refreshed!
- Personality, taste, smell is not persistent.
友達はさっぱりした性格で、一緒にいて気が楽だ。
My friends are easy-going and easy to be with.
このドレッシングは、さっぱりしていておいしい。
This dressing is refreshing and delicious.
- さっぱり + negative form, "not at all".
さっぱり思い出せない。
I can't remember at all.
すっかり
- A situation where nothing is left.
れいぞうこの中の食べ物がすっかりなくなってしまった。
The food in the refrigerator is completely gone.
- Being in a certain state completely.
テストがあることをすっかり忘れていた。
I completely forgot there was a test.
もうすっかり秋だ。
It's already completely autumn.