1. Acetaminophen is more likely to kill you. Its therapeutic index is very low - that is, the dose that makes you feel better is uncomfortably close to the dose that'll really muck you up. It's often sold in 500mg tablets; many people reflexively take two. The maximum daily dose is cited as 4g, with 7-10g (150mg/kg) being toxic in most people. Toxicity doesn't necessarily mean death, but it does mean that you're going to be looking for a new liver, which is less than fun. Acetaminophen OD is the leading cause of liver failure in the Western world. Oh - chronic use will decrease your lung function and may give you COPD.
Ibuprofen toxicity is not particularly rare, but it takes more doing: therapeutic dose is 200-400mg, with acute toxicity at 300-400mg/kg. Fewer than ten known ibuprofen OD fatalities have been reported, and most of these probably aren't. More likely is that you'll damage your GI tract with continuous use; the COX-1 inhibition decreases mucus production in your innards, which is unfortunate since it's the COX-2 inhibition that does all the good stuff. Oh, and like all NSAIDs, it increases your chance of having a heart attack (think Vioxx) and may eventually decrease kidney function.
2. Ibuprofen is an analgesic and anti-inflammatory; Acetaminophen is only an analgesic. If you have sporty pain, it's probably partly because of inflammation, for which acetaminophen will do nothing.
3. Ibuprofen's effects last longer, generally speaking.