I continue to read all these debates between the different sizes, as if one size is all around better in some way. I have had the privilege of having all 3 sizes, and figured I would post my experience and compare them...
7.9"
I used the iPad Mini 2 for a couple of years, and I think this is this is the best size for most gaming. As it's the lightest, it's the easiest to hold in your hands for long periods of time. For this reason I also think it's the best size to use while in bed or while laying down. It's obviously also the most portable. For web browsing I found it to be a bit small in the portrait orientation and often had to turn it to landscape if I wanted to view regular (non-mobile) websites, which then cuts down significantly on how much of a web page you can see at one time. Also, sound quality and volume is not much better than an iPhone. I also really preferred using this size iPad when traveling and on a plane, train or bus. It's really easy to just put in your coat pocket and doesn't take up much space in your bag either.
9.7"
I used the iPad 2 for a couple of years back in 2012-2013. I suppose this size is the best all around size. It's small enough to hold for long periods of time, but large enough to comfortably browse the web with. Gaming is also good on this one, although some fatigue does set in after a while from the extra weight over the iPad Mini. The new 9.7" iPads weigh less than the iPad 2 did, so this probably is even less of an issue than before, but there is still some extra weight over the iPad Mini. While my iPad 2 did not have split screen viewing back then, I did try this feature out with the iPad Air 2 in the Apple Store, and it is really cramped when trying to use 2 apps side by side that it is best for use in a pinch. You wouldn't want to sit there with 2 apps open for long periods of time, especially if one of the 2 open apps is Safari. But I could see using the feature to respond to a message or to check my email without having to close what I'm doing.
12.9"
I now own the 12.9" iPad Pro. To begin with, it is somewhat useless for most games for 2 reasons. Most games with on screen controllers have not optimized the app for the large screen, so unless you have giant hands, it can be impossible to reach the controls with your fingers. Also, holding the large iPad Pro in your hands for long periods of time is NOT comfortable. Fatigue sets in after a short while. Now for the good.... The large iPad is best when used on a desk or table, or on your lap while sitting down or laying on a sofa.
Adding the Apple Smart Keyboard, it can indeed be a laptop replacement for many, including me! This coming week I'm going to put my MacBook Pro up for sale. I've decided to use the iPad Pro as my main computer. I still have access to a PC at work for the occasional task that requires a "real" computer (such as taking a file off a USB stick drive). Between the Microsoft Office apps and some other utility apps I've found in the App Store, I can do 99% of what I need to do, and I've decided it doesn't pay to keep my MacBook (or replace it).
I don't miss the 9.7" iPad at all, but I will admit that I miss the iPad Mini for gaming. So I have decided that when the iPhone 7 comes out, I'm going to try the "plus" model. I think with the large 5.5" screen, it will be close enough to the Mini that it should provide a good gaming experience.
What I would suggest to anyone debating which size to get is to look at your other devices and get something in the "middle". For example, if you already have a small laptop, then maybe an iPad Mini or 9.7" iPad would be a good fit for you. If you have an iPhone 6 Plus and an iMac but no laptop, then maybe the 9.7" or 12.9" Pro would be a good fit.
All of the iPads are great devices and they all are the "best" for one task or another.
7.9"
I used the iPad Mini 2 for a couple of years, and I think this is this is the best size for most gaming. As it's the lightest, it's the easiest to hold in your hands for long periods of time. For this reason I also think it's the best size to use while in bed or while laying down. It's obviously also the most portable. For web browsing I found it to be a bit small in the portrait orientation and often had to turn it to landscape if I wanted to view regular (non-mobile) websites, which then cuts down significantly on how much of a web page you can see at one time. Also, sound quality and volume is not much better than an iPhone. I also really preferred using this size iPad when traveling and on a plane, train or bus. It's really easy to just put in your coat pocket and doesn't take up much space in your bag either.
9.7"
I used the iPad 2 for a couple of years back in 2012-2013. I suppose this size is the best all around size. It's small enough to hold for long periods of time, but large enough to comfortably browse the web with. Gaming is also good on this one, although some fatigue does set in after a while from the extra weight over the iPad Mini. The new 9.7" iPads weigh less than the iPad 2 did, so this probably is even less of an issue than before, but there is still some extra weight over the iPad Mini. While my iPad 2 did not have split screen viewing back then, I did try this feature out with the iPad Air 2 in the Apple Store, and it is really cramped when trying to use 2 apps side by side that it is best for use in a pinch. You wouldn't want to sit there with 2 apps open for long periods of time, especially if one of the 2 open apps is Safari. But I could see using the feature to respond to a message or to check my email without having to close what I'm doing.
12.9"
I now own the 12.9" iPad Pro. To begin with, it is somewhat useless for most games for 2 reasons. Most games with on screen controllers have not optimized the app for the large screen, so unless you have giant hands, it can be impossible to reach the controls with your fingers. Also, holding the large iPad Pro in your hands for long periods of time is NOT comfortable. Fatigue sets in after a short while. Now for the good.... The large iPad is best when used on a desk or table, or on your lap while sitting down or laying on a sofa.
Adding the Apple Smart Keyboard, it can indeed be a laptop replacement for many, including me! This coming week I'm going to put my MacBook Pro up for sale. I've decided to use the iPad Pro as my main computer. I still have access to a PC at work for the occasional task that requires a "real" computer (such as taking a file off a USB stick drive). Between the Microsoft Office apps and some other utility apps I've found in the App Store, I can do 99% of what I need to do, and I've decided it doesn't pay to keep my MacBook (or replace it).
I don't miss the 9.7" iPad at all, but I will admit that I miss the iPad Mini for gaming. So I have decided that when the iPhone 7 comes out, I'm going to try the "plus" model. I think with the large 5.5" screen, it will be close enough to the Mini that it should provide a good gaming experience.
What I would suggest to anyone debating which size to get is to look at your other devices and get something in the "middle". For example, if you already have a small laptop, then maybe an iPad Mini or 9.7" iPad would be a good fit for you. If you have an iPhone 6 Plus and an iMac but no laptop, then maybe the 9.7" or 12.9" Pro would be a good fit.
All of the iPads are great devices and they all are the "best" for one task or another.
