Hard choice.
Immortality
Advantages
- Live forever!
- Watch the world move.
- See more of the world than anyone else, if you're relatively lucky.
- Meet more people, have more relationships, and in general: really live more.
- Opportunity for riches is huge. We're talking... ruling the world and living in a chocolate palace, here.
Disadvantages
- Watch your friends grow old and die, one by one. Yippee?
- Having it virtually guarantees that your death will be violent.
- If you're locked up for "life", that's a long, long time. Of course, the chains will rot eventually... unless you're in a nuclear vault. Then you'll probably come out when a new race makes you look redundant. Cue more imprisonment - you'd be the new King Kong.
- If something truly breaks you, you'd be broken forever, rather than being allowed the peace of death. Unless you suicide, which is an unpleasant way to go.
Invincibility
Advantages
- Look maw, no death! Yet...
- You can probably become a military superweapon, if you're into that sort of thing.
- Riches ensue.
Disadvantages
- If you are locked up, what will you do? Being invincible doesn't mean unsealable.
- How exactly are you going to have surgery for old age issues when you're invincible? They can't exactly cut you open... so your life expectancy is probably half that of everyone else.
After looking at the disadvantages of these, and the extremes of possibility posed by each, I think I'd say: neither. Living life without such unnatural additions is a philosophically strong standpoint.
Besides, it'd be hard to be motivated if you had something like this keeping you from dying. Survival instinct is, after all, what drives us.
Of course, if you'd said we'd be able to control these powers at will, I'd choose one. Probably immortality in that case. Because being able to decide to start aging is just better.
Internet Kraken said:
Certain things in life are only exciting because they are dangerous. If they no longer pose a threat to you, then they won't be as thrilling. Jumping off cliffs and absorbing bullets will get boring at some point.
I'm sorry (and it's possible that in five pages someone thought to tell you), but if this were true, would we play video games?