I have several vintage transistor portables, 1970s vintage for the most part. Every one of them works as well as can be expected. My Zenith R-70 AM/FM from 1980 is built to last, like all Zeniths, despite the fact that most of it is on a PC board. The radio itself runs on three C-size batteries that seem to go on and on and on . . . I put a set of batteries in it a couple days after I won the radio in an ebay auction six months ago, and they are still good. The radio sounds great as well, even with its 4" speaker, but again that is (or was) Zenith for you.
I also have a Zenith TransOceanic Royal 1000, another ebay score, that works, and well, but the dial cord snapped several months ago, so I have a repair job to do on it this winter. The set doesn't use much power; the only time I ever had to replace the batteries in a year or so of owning the radio was when the AC adapter plug on the side of the cabinet developed a short, putting a direct short across the battery pack and draining the cells in a matter of hours. I replaced the batteries and repaired the shorted wall-wart socket; that did it. In a year my TO is only on its second set of batteries, although I don't use it much these days.
Also in my collection of vintage portables are two Sonys, a TFM-7720 AM/FM and an MR-9700W AM/FM stereo set, both 1973 vintage. Both radios work well for their age (over 30 years now). One thing that struck me as odd about the TFM-7720 was the fact that it uses two D-size batteries for DC power, whereas most portables I've seen use at least four such cells in series for six volts. The TFM-7720 is the first three-volt full-size portable radio I've seen to date, although I have seen a few smaller transistor pocket radios that run on two AA or even AAA batteries; I have a small FM stereo scan radio that runs on two AAA cells and have also seen other models of these scan radios that run on the small round watch batteries, or even hard-wired lithium cells (many of these portables now sell for very low prices in discount and dollar stores, so in many cases the battery could cost more than the radio itself; this is probably why the batteries are hard-wired into the sets--when the battery goes, just throw the whole thing in the trash and get a new one).
The last portable (full size) in my collection is an Aiwa AR-115 from 1967. The last time I tried it, it worked, but I don't know about now, as I haven't had it running in several years. This radio sounds good with its 4" speaker, but it doesn't have a tone control as does my Zenith R-70. If I were to do an A/B comparison test between the R-70 and the AR-115, the R-70 might be the better-sounding radio, as it has a push-pull audio stage. The R-70 is also, IMHO, much more sensitive and selective than the AR-115 or any other transistor portable I own, since the R-70 has two ceramic filters, one for AM and one for FM, as well as four FM IF stages and two IFs on AM. I honestly believe this was one of the last really good transistor portables Zenith made before it went out of the radio business in the early 1980s.
As to the comment regarding 1950s batteries leaking "like a sieve" that another poster made here: Today's batteries are better than cells made even 30 years ago, but they still aren't leakproof--they will still leak and make the devil of a mess if they are allowed to run down and are left in a device for months or years (!) after they go dead. I have a Panasonic boom box I rescued from a trash pile last summer that had six alkaline batteries (Eveready Energizers, IIRC) in it, all of which had leaked and made a mess inside the battery compartment when I found the unit. I guess the former owner just left the old, exhausted batteries in it and forgot about it, which is almost always a one-way ticket to disaster when the cells eventually leak all over the inside of the battery case--many times this will ruin the device in no time flat. Fortunately, the battery compartment cleaned up nicely (the terminals were not damaged), although I haven't yet tried the boombox on batteries as the battery compartment cover was and still is missing; the unit works well, however, on AC power.
BTW, I also had a Zenith Royal 500 in the '70s, a thrift-shop find, that worked well for most of the time I had it. I don't remember anymore what happened to it to cause me to get rid of it, though.
Also had a Zenith Royal 820 (another thrift-store find) in the '80s. It too worked well (and sounded great) for most of the time I owned it, but eventually the dial cord broke and something else went wrong, so I got rid of that one as well. I wish I hadn't, though. Oh well. One of these days I'm bound to find another Royal 500; they show up on ebay these days quite a bit, in various colors.
I have only seen one Royal 500 on ebay with a broken cabinet; that speaks volumes for the unbreakable nature of the cabinets used to house these radios. The sets often have the usual signs of wear, such as scuff marks and scratches, but other than the one I just mentioned, I haven't yet seen another Royal 500 with a broken cabinet.
Those were the days.