As a rule of thumb, the wider a track is, the better it’s going to sound. Ditto for tape speed. Faster speeds=better sound. Theoretically, a 1/4” reel-to-reel 4-track running at 7 1/2 IPS is going to sound better than a 4-track cassette running at 3.75. A 1/2” 8-track running at 15 IPS will sound better than a 1/4” 8-track running at 15 IPS.
But in reality, it will depend on a lot of other factors, such as the quality of the tape and condition of the deck in use. A lightly-used Tascam Portastudio might sound better than a 1/2” 8-track that has been poorly maintained. Sometimes a deck merely needs a good cleaning, head-alignment, or properly biasing for the tape being used. Other times, the heads may too worn to produce acceptable results.
Also, it’s worth noting that when old pros say they like the sound of tape, they are not likely referring to “affordable” machines like, say, a Tascam TRS-8 or Fostex R8, but to the expensive, high end machines they’ve used in studios that kept their gear well-maintained. Tastes and applications have changed and today many people love the lo-if qualities imparted by the cheaper machines. I tend to fall into this latter group. When I use tape machines, it’s because I want to hear their effect on my sound.
For me, a 4-track Tascam Portastudio is often the best way to go. When I need a little more, I might turn to the Fostex A8 reel-to-reel. Most of my other, better quality decks have become too undependable and I don’t want to keep throwing money at them, so they sit in storage. As much as it pains me to say so, once this old Fostex gives up the ghost, I will likely not replace it.
One other point: it’s all but impossible to get a new chrome-based cassette of the sort Portastudios were designed - and biased - to use. Stuffing a normal bias cassette into a 4-track is going to produce a lower-fidelity recording than using the chrome (not metal) tape for which it was designed. As any 4-tracker knows, tapes like Maxell XLS-II and TDK SMPro are getting hard to find on the used market - especially the shorter ones best-suited for 4-track machines. And NOS tapes are getting costly on the used market.
On the other hand, pro-quality reel-tapes are still being produced and sold and most of the more-commonly used pro tapes such as Ampex 456 and 499 are directly replaceable. Mind you, you’re going to pay over $30 per reel in most cases, but it’s nice to know you can crack open a fresh tape that hasn’t been slowing turning to goo in a dark cupboard for the past three decades…