I tried a bunch of them including Gtasks and Remember the milk. while RTM was pretty good, I'm not interested in paying 20 bucks to use it. Just not worth it to me when there are so many programs out there to do this....
After experimenting, i decided to use google calendar to accomplish this. This way, I have one location I can go to when I'm on my laptop OR on my phone. I created a new calendar called Tasks. So I have my main calendar and my tasks calendar. My main calendar is blue and my tasks are green.
When I want to create a task, I can either use the Calendar app on my phone or create it on gmail through the web interface. I create an all day event and label it whatever.
So now, when I open the calendar app on the phone, all my tasks are in green and all my appointments are in blue. It's the same on the gmail web interface. The cool thing about it is that the tasks stay at the top of the day I'm looking at and don't interfere with my appointments. Once I'm done with one, I just delete it. You can set reminders if you want to but I don't do that with tasks because I look at them all the time to make sure I get them all done for whatever day I'm on...
On top of all that, if you go to gmail calendar through the web interface on your phone, it has a very easy to read intuitive interface there. I love it, and can easily distinguish between tasks and appointments. I can edit them from any interface I want and everything is synced automagically.
So with all of those apps out there, I found that I don't need any of them. This is much easier for me. I also use google docs for my business, mail and calendar so no matter what I'm doing, I have access to everything.
A bonus feature to this is if you put the location on a task or appointment, you can bring up a map on your phone or your computer and get directions or see satellite view.