If you are considering enrolling in Tai Chi beginner classes such as those you can find in Portland Oregon, you are going to find that as with most Chinese martial arts, there are several different styles such as Yang Style, Chen Style, Wu Style and Sun Style. Each of these is very well known and there are large numbers of people practicing them. At the same time they each have their own forms, some of which are easy to learn, while others are somewhat complicated and can take some time to master.
As to which particular style of Tai Chi Chuan might be best for a beginner, you need to start by realizing that all of the styles are considered to be good for your overall mental and physical health. While this may not exactly be the answer you are looking for to help you choose which style of Taiji will be the best one for you to learn as a beginner, it leaves the field wide open rather than trying to tell you blatantly that Yang Style is much easier to learn than say Wu Style.
What you do need to realize is that while each of the different styles are interlinked with each other in as much as they share the same basic theories and skills, you will find that they differ significantly with regard to the forms practiced. With this in mind, most instructors will tell you that you should spend a fair amount of time studying each style and its associated forms, skills and tricks. This will help you to become familiar with each of them and as such be able to determine which of them interests you the most.
Typical Tai Chi Beginner
Most beginners will find that it makes sense to begin with a less demanding style such as Yang and then as your skills and physical health improve, you can always move up to one of the more challenging styles. You can also to talk to several instructors and ask them for guidance to help you choose the best Tai Chi beginner style to fit your interests and current state of physical health.