I know others have suggested hiring to try out different pumps to figure out what you want to buy, just wanted to let you know that this probably isn't practical.
The pumps you can hire are hospital grade. They cost upwards of $3000 to purchase, which is why they are so expensive to hire compared to buying one that is for personal use. They are so expensive because they are designed to be used 8-12 times a day, every day for years. If you used a personal pump in this way (with the exception of something like the medela freestyle, which costs around $680) it would burn out within 12 months.
It is not possible to hire personal use pumps, as they are not sealed internally like hospital pumps are, meaning that there is a small risk of your milk coming into contact with someone elses milk. There is no risk of this with hospital grade pumps.
Even though the chances of anything bad happening if your milk came into contact with someone elses are very very very close to zero, it is not possible for pump hirers to get insurance on personal grade pumps for this reason.
It really depends why you are expressing as to which pump is best!
Hope that helps.
The only thing I can suggest is asking around if you have any friends who have a pump you can try