Trying out instruments is never an easy task, but you are going about it the right way by trying many of them to see what you like. I always recommend that string players search a while and make no rash decisions when it comes to choosing an instrument. It is good to have colleagues play as well, but don't get their opinions on the instrument, just hear them playing it and make your own judgement. Remember, you are the one who will be shelling out the money for the cello and only you need to be completely satisfied with it. Often, another player can be critical of another instrument simply because it is different from theirs - the one they chose as perfect for them at the time.
Even if you don't find THE cello for you in all the ones you are currently trying, you will find qualities you are looking for and soon your search will be very focused according to more specific needs. When you are narrowing down, it is good to get second opinions regarding price by looking up price history (auction and private sales) and getting verbal appraisals from other dealers, making sure not to tell them you are looking to buy this instrument as the appraisal will be tainted one way or the other.
Lastly, feel free to ask your fellow cellists on this board about their recommendations on celli in that price range or specifically on the maker you are preferring at the time. There might be someone out here with some experience as an owner of a similar cello that you might be selecting.
Todd French