It may be prudent to test drive many but you may find your dream machine after only trying out a couple. I bought an Innova after test driving only that and and an HQ sweet 16.
See if there is a quilt shop around you that offers training on a LA. Many that rent LA time offer a training class that you must take before renting. This is the ideal way to learn if you even WANT to LA. The training will have you load a quilt on the rack then try different techniques like FMQ, following a stencil or drawn line, following a pattern with a laser light, like a panto and some even have Stylus type systems like Groovy Boards or Circle Lord.
If a quilt shop that does rental is not available find if there is a LA dealer near you and see if they offer any kind of training like that. Many do at a charge and you are under no obligation to buy from them after taking the class (Usually around $50 or $60). IMHO a good dealer is an invaluable asset to have. You have near by support, Many will come to your home and install the machine and give you a hands on run through and you have a familiar source for gadgets and notions like needles, bobbins, etc.
By taking a class, this will give you a good idea if you want to pursue this investment. I have heard some people don't like the effort it takes to load a quilt, others think they can't stand at the rack for many hours at a time. Some realize right away that LA is not for them. Others realize this is exactly what they have imagined and can't wait to get one. Yes LA are very expensive. But you definitely get what you pay for.
Most people who make this investment do their research and take about a year to decide. This gives you ample opportunity to find a major show where there may be several LA vendors so you can test drive different machines. You need to decide on a budget. There are low end streched machines like Baileys for a few thousand (only phone support unless you live in upstate NY near them) all the way on up to fully robotic models that cost upwards of $30K and more!. A good machine and rack will definitely make a difference in your learning curve and in your enjoyment of LA quilting. As will extras like a stitch regulator.
You could also see if there is a machine quilting expo coming your way in the near future and take a class at that. Many offer beginner classes that could also help you decide.