Using the app and the camera... A hybrid approach!
The folks at iNat have done a really great job on the app.
I've been bumping up my observations lately by using the app. In the past, I wasn't too crazy about the app, solely based on the image quality that I got from my iPhone. Well, either the app improved or my camera on a newer iPhone improved, but now I use that a bunch! The image quality is pretty good, especially after clicking "large" or "original" on the image. It's quick to observe too -- just a couple touches on the iPhone. I try to only observe organisms that I'm fairly certain of the ID with the app... A lot of these are the "common weeds." Despite the commonness, I still want to document their existence in space and time. :)
As I was trained in the herbarium, a fertile specimen is a good specimen, so I try to only observe plants with flowers or fruits. Most if not all good keys use these reproductive structures. So, I think it's important to get flowers or fruits with my observations.
Now, I use my camera (nothing spectacular -- it's a Nikon Coolpix P530) on most moving critters -- dragonflies, birds, mammals, etc... I do this for the zoom capacity and the image quality. I'll crop the photos with the camera too (I used to not do this, and I'm sure it was fairly annoying to see my observations). I also use my camera on the plants that I'm not certain about -- or weird unique ones that I'm unfamiliar with. It takes a lot longer to upload these, as I manually put in the location and maybe write a little bit about the observation, but it's worth it to learn a little more about the organisms.
I try to take a few images for each observation too -- if it's an organism I don't know, I'm not sure which angles are important... So I try to take several! Trust me, not all of them turn out great... But hopefully a few are usable.. :)
So, do you use the app or a camera or both? If you only use one or the other, try using both!