I think either Ensure or Ensure Plus would be fine. Ensure Plus has even been documented to induce remission in some patients who in been steroid-dependent for years.
I wouldn’t worry too much about sugar in the formulas. Our body breaks down all carbohydrates we eat into simple sugars anyway. Sugar isn’t bad for you in itself; the problem is that foods that are high in sugar are often low in other nutrients and high in fats, and therefore high in calories. Enteral nutrition formulas contain sugar as an energy source, which our body needs, but also contain all the vitamins and minerals we need.
Using these liquid diets can actually reduce inflammation and decrease levels of inflammatory cytokines, so I wouldn’t worry about drinking as much Ensure as you can handle. In fact, a case study was just published a few weeks ago reporting on a woman with Crohn’s, psoriasis, and scleritis, who either didn’t respond or lost response to all the standard Crohn’s medications, including Remicade, and then had a spectacularly good response to enteral nutrition (Crohn’s symptoms cleared up, psoriasis healed, and eyesight returned) (http://www.ncbi.nlm.nih.gov/pubmed/18344883?ordinalpos=1&itool=EntrezSystem2.PEntrez.Pubmed.Pubmed_ResultsPanel.Pubmed_RVDocSum).
She was on the liquid diet exclusively for five weeks (with improvement beginning after the first four days), and since then has been able to maintain remission using two meals a day of the liquid formula and two regular meals per day. The formula she used was Modulen IBD (which does contain sugar, by the way). This particular formula is not currently available in the US, but enteral nutrition formulas all seem to work about equally well.
Hope this helps.