I defer to all the agents here who are speaking directly to the housing situation in and around Portland, the relative pricing points for single family homes versus townhouses, and so on.
However, let's clear up some misconceptions:
At least three answers warned about the drawbacks of condos. So what? Not all townhouses are condos. A "condominium" is a form of legal ownership, and can apply to multiple units in one building (like an apartment building), to townhouses, and even to single-family homes. A townhouse describes a type of structure--usually a multi-level property with 1 or two shared walls. Condos and townhouses are NOT the same. (In fact, many of the townhouse complexes around where I live are not condos. They do have a homeowner's association, but that is very different from a condominium.) So: Don't be scared off by condo concerns when you might not even be buying a condo.
One piece of advice below seems to be confusing HOA fees with condo fees. ("Homeowners Association Fees are much higher in Condominium complexes due to the "Common Areas.") They're two different things. Further, the logic doesn't hold. There are likely to be common areas, to one degree or another, in any complex. More elaborate ones will have more green space (that needs to be maintained), maybe a pool, maybe a club house, maybe gated security, maybe snow removal, and so on. That all will be paid for, one way or another. There's nothing about a condo that makes the swimming pool more expensive to maintain than in a non-condo development. You think the utility company charges more for a gallon of water if the condo is using it? I don't think so. Bottom line: The more amenities you receive, the more you're likely to pay, regardless of ownership type.
Very good advice below from Steve. Sound transmission depends in large part on construction--and that depends, in part, on what the building code requires. His advice about an end-unit townhouse is excellent. But even with an interior townhouse, the noise transmission will be less than in an apartment--not just better sound control horizontally, but no concerns about annoying your neighbors (or visa versa) above or below you.
As for being best suited as starter homes or for downsizing, maybe that's a regional thing. That's certainly not the case in many areas of the country. I know plenty of townhouse developments in the Washington area where people have lived for 15-20 years or more, raising families, sending kids off to college. It also depends on the size of the townhouse. A close relative of mine owns one in Northern Virginia. Upstairs, it has 3 bedrooms and 2 full baths. On the main level, it has a good-sized kitchen, dining room, and living room. Downstairs, it has a large rec room, an extra room that's being used as a home office, and the laundry facilities. There's also storage space both in the basement and tucked under stairways. It's an end unit, so it has windows and yard on 3 sides. It has over 2,000 square feet of liveable space. That sort of property is big enough for plenty of families. Not everyone needs a McMansion.
So, don't be scared off by the concerns you listed, or by some of those below.
Instead, take a look at both townhouses and single-family homes. See what you can buy for the money. Also, get a feel for the neighborhood. (Sure, there are townhouse complexes I wouldn't want to live in. But plenty of others that would be fine.) And talk to the residents. Ask how they like living there--what the good points and bad points are. That's really the best way to decide.
Hope that helps.