Jim at thefilterguys will more than happily help you make the right choice.
It is recommended to hook up after the water softener.
I personally would choose one with the canister sized DI vs. the inline DI.
Depending on your budget, any of the units with full size DI cartridge you can't go wrong with. Of the features probably that matter the most is the auto shutoff valve, and the inline TDS meters, and decide to get second DI or not. All of which can easily be upgraded later if your wanting to save on the initial cost now. All of them have high quality filters so there are no real concerns with one producing better water than the other.
It is really nice to have the second DI so that you can fully exhaust the first one without effecting water quality. Even if you use
Color changing resin to determine with DI is exhausted you will find that if still has some life in it even when the color show exhausted so nice to have the second unit to back it up. Nothing says you can't add a second DI unit later if you want to keep the costs down initially.
Also keep in mind that our water supply usually has quite a bit of iron in it so the
sediment filter has to be replace more often than other parts of the country. Probably a good idea to order a few extra of those ( $3 each ) to replace when they start appearing to be red about 3 months of so.
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