These are very similarly sized devices. The iPad is the slightly larger of the two, but there's not more than a couple of millimeters' difference in any dimension.
If you're concerned about fatigue from holding the tablet in one hand, the iPad is also the weightier of the two, but only by a slim margin. Its Wi-Fi-only and WiFi + LTE variants are about 2-percent heavier than their Tab S3 counterparts.
The Tab S3 has a glass back panel, which might look nice, but could be less practical on a handheld device than the iPad's aluminum unibody.
The Tab S3 will be available in three colors, but Samsung has yet to confirm which variants will be available to US customers. The iPad Pro is available in four different metallic finishes.
The two displays are identically sized.
They also have identical resolution. Resolution isn't the only measure of a screen's quality, but without doing a side-by-side look, it would be hard to say which one is more attractive.
Both tablets have a fingerprint sensor for security.
They're also both available in Wi-Fi-only or (more expensive) Wi-Fi plus LTE variants. the Wi-Fi Tab S3, however, will launch first, with the LTE model arriving at an unknown later date.
Both makers designed these tablets to play nice with an optional add-on keyboard cover (sold separately).
They also both support active stylus input, but Samsung includes the S Pen stylus with the Tab S3, while the Apple Pencil is sold a la carte for US$99. The S Pen does not need any charging, but the Apple Pencil charges through the iPad's Lightning port.
Samsung opts for a capable Qualcomm-made processor, while Apple manufactures its own.
The Tab S3 has twice the RAM, but to be fair, Android and iOS devices use RAM differently.
The iPad Pro is available in three sizes, but the Tab S3 is only available with 32 GB of built-in storage.
However, the Tab S3 has a microSD slot for expansion up to 256 GB. Good luck finding a microSD slot on an Apple device.
The Tab S3 adds in one additional megapixel in its rear camera.
The iPad's battery is bigger, but there are many factors that go into overall battery life.
Both tablets have four audio speakers.
Both operating systems allow for split-screen multitasking, so you can use either tablet to use two apps at once.
Samsung has not yet confirmed US availability yet, but we do know that the Tab S3 goes up for pre-sale in the UK on March 17, to hit shelves on March 31. We expect it to hit other markets not too long after that.
Samsung has not officially confirmed US pricing, but just for projection's sake, the previous generation Tab S2 had a starting retail price of $499.