Will they be updated in September ?
Which is better for portability and general Web serfing and stuff what are the spec differences
Most iPads are updated in October. Based on rumors, the larger iPad will probably receive an update, although we don't yet know what the changes will be. It's unclear if the smaller iPad Pro will be updated, as it's a fair bit newer. If you can afford to wait, then wait; you have about 1-2 months to find out if they'll be getting updates, at which time you would either be able to get the latest and greatest, or pick up the current generation at a discounted cost.
For portability, the smaller iPad will always win out. The larger iPad is surprisingly light, but the size makes it a bit cumbersome to bring about and to hold in your hand for extended periods of time. Holding with two hands or propping it against something is more manageable, but if you wanted to hold with one hand and write with your other (notepad-style), it's very difficult to do.
From a hardware standpoint, the smaller variant has 2 GB of RAM and its processor and graphics chip are clocked slightly slower (2.16 GHz, vs 2.26 GHz). The larger iPad has 4 GB of RAM - the most of any iOS device at present. You can juggle 4-7 apps without needing to reload them (depending on the apps, of course), and when they do, it's incredibly quick.
The optimal device depends on your intended usage. If you're looking to have a device to carry around the house and rarely take outside, then size doesn't matter much; if you want something to use while you're out and about, the smaller device has the advantage. If you're looking to use the Apple Pencil, the larger device has the advantage if you're looking to do graphical work; for writing, there's no clear advantage to either (unless you're trying to write on the device while holding it with one hand, in which case the smaller device wins). As far as use as a laptop replacement, the larger iPad's type cover has larger keys, which may be more comfortable to type on. For performance, it's difficult to say whether you'd really notice a difference in your day-to-day usage, but the larger iPad Pro is the absolute best you can get in speed and overall performance. I don't know that the increased cost is justified by having Safari tabs reload just a bit less frequently, though.
Just one more note about the size. We tend to talk about the devices in terms of their screen size, but the physical dimensions of the iPads are larger owing to the top and bottom that includes the camera and fingerprint sensor. The larger iPad Pro is 1-2 inches longer than the Retina MacBook, despite having a screen size that measures the same diagonal size (12.9" vs. 13" for the MacBook). It's still amazingly more nimble than how laptops were even just a few years ago, but compared to the current generation of mobile devices, it's probably one of the least portable.
it's up to you if you want a bigger screen or more portiablity.
