Any of the portable units would work just fine. Research their construction and ease of regeneration and see what would work for you. As already mentioned, water hardness determines how much water will be treated before regeneration and larger capacity was a consideration for us. We have been using the
ABCwaters 16,000 grain unit and selected it because of the robust construction of the handle and water connections that were all brass instead of plastic like many others. I did an onboard install as I did not want to leave the softener outside and further, I really wanted to retain being able to still use my hose reel to make only one connection to city water without additional hoses. Now, all water from my hose goes directly to the softener and I have a flow meter that I can monitor how much water is being used. I test the city water hardness and then can calculate how much capacity I have left in my softener before regenerating. More involved getting it plumbed initially than simply setting the portable unit outside but, I really like the convenience now that I have everything installed. I have details of my installation on our Blog if you're interested. Just one way to do it and it works for us.