I like answering language- and lingusitics-oriented questions (like "Can anybody decipher this Japanese?" and "What are the main differences you notice between American English and British English?" and "What was the Mandan and Welsh language connection theorized by Goerge Catlin?"), but those questions are unfortunately rather rare.

Aside from those, I like open-ended questions that anyone can answer (like "How are you doing / Please answer as a haiku / This should be quite fun" and "What food do you think best represents America?"). I like more specific questions too, ones that are simple enough that I can research without knowing anything about the subject (like "How many Tintin books were published by Hergé?"), and stuff I can answer with my own experiences as well (like "Have you ever listened to a book-on-tape audiobook?" and "Can you help me with ways to study effectively?").

I'm all over the map, really. :)

But I answer because I like answering questions, and because I enjoy explaining things to people - not specifically because of the tips (though it's nice to get paid for doing something I'd already do on Yahoo! Answers). If I see something I know the answer to, I'll go for it. I don't browse the Highest Tips board, though I probably would earn a bit more.

As for your other question - I find that most people go with the default tip most of the time. And those who do offer a higher tip can do so on any question, there's no real pattern to it. The staff may ask some high-tipped questions about current events and technology, but they're not the majority of well-paying answers, I don't think.

Personally i like music questions, really its one of the only things i feel i always know the answer too and i would say its my expertise. Probably the only thing i feel confident about 100% of the time. Other than that its a mix bag of trivia knowledge. For example i just answered two questions from @davepamn about liver functions and the effects of alcohol. Its pure chance that i know about it and Dave asked about it, I actually failed biology every time i ever took a class on it so I'm no expert. Random little interests i had years ago come back when someone asks a question like that. So really thats why i answer questions, i feel it helps me remember things i learned but really have no chance to think about them. I tend to start to forget this knowledge, answers that catch my eye almost always refresh my memory. I like the open ended questions of opinion but I'm a natural debater and sometimes feel bad for always disagreeing with people.

Also i try to avoid high tip questions because usually there are so many answers my opinion is already on the thread just in different words than i would use. Nothing grinds my gears more on mahalo than people not reading the answers before they post their own. I always go straight to the bottom for new and un answered questions. This seems to be the best way for me to make tips, i made 10 best answers the other day while i lost a contest answer for 10 dollars, it evens itself out. If i focused on trying to get that 10 M$ i would have lost out on all the points and all the interesting 50 cent questions out there. The way i see it, answering a question with a small tip and no other answers is like finding the money on the ground, trying to get the 5-10 dollar questions is like entering your name in a raffle. (IE all the Does Obama deserve a second term answers)

I like technology based questions.I give answers to these question for a fun but for making money these questions are not too good they make a very little money.