First off, make sure you are comfortable in the spa. Make sure you fit the model you are considering. The wet test is a good idea once you have narrowed your selection to a few spas. More jets is not always a good thing but a marketing tool. I generally use my spa on high speed for a few minutes and then back to low speed or with the large whirlpool jet. After a while, the high speed jets can make your back sting.
My personal opinion and experience is to keep the spa as simple as possible. Whever clients chose fiber optic lights, tv, stereo options... those are the items that failed and required the most maintenance.
As far as dealers, on the high end you will find 5 years equipment / no trip charge as your warranty. As you drop in price, so will your warranty BUT the reality is that in some cases you are prepaying for your warranty. For example, most larger spa companies have thier premium line and a basic line. Hot Springs / Tiger River.
Avoid buying your spa at Sams Club, Home Depot, or Lowes... buy it from a dealer but know that you are either buying the warranty up front or paying for it later.
Find a chemical maintenance system that works for you and your bathing load. Find a chemical supplier you trust, not Walmart or Home Depot. Most clients bad experiences come from poor water maintenance.
Also, basic water chemistry + frequent water changes and proper balancing of the spa can eliminate MOST of your long term problems