oh i couldn't make it through Lost in Translation. it was so bad in my opinion. i did not think it was funny at all. this was a DVD rental as well so i just returned it. neither my partner, my neighbor nor myself liked it. so i wouldn't recommend wasting your time on this.
american splendor i haven't seen so i can't vouch for it.
I don't think you can compare those two movies. American Splendor is almost a documentary with some good laughs in it. Very good movie but I wouldn't say it's a laugh fest.
Lost in Translation was a great movie. It's light comedy but it's got great atmosphere. Bill Murray does an awesome job. I'd say if you liked Punch Drunk Love you like this movie. Very similar in type of humor I think.
I liked Lost in Translation better then American Splendor but not by much.
If you want a good movie try to find the movie Grass. It's a documentary on how marijuana became illegal and what the government has done through the years. It's hilarious! Narrated by Woody Harrilson (dude from Cheers). All the footage they have from back in the day is just too funny to see.