Ideally, a beginner should have a nice inexpensive, older, well tuned dovetail saw, but since that would require an old timer to check the saw out and maybe tune it up, that usually isn’t practical. With that exception, my first choice for a true beginner would be the Veritas dovetail saw for the following reasons:
A true beginner will be developing their feel for the wood and the tools and with western saws with a traditional style grip it is easier to develop a sense of blade orientation for repeat cuts. The grips on Japanese and gents saws give you less feedback to help you maintain the correct orientation. Beginners tend to get little wild with their sawing action and thinner saw plates will be damaged easier. The plates on the Veritas saws are thick enough to generally resist any reasonable use. While the plates on some older saws may be thicker, they more often than not will need tuning and the true beginner won’t be able to tune them or know when they need tuning. A new brand name saw should work well straight from the box and will help the beginner learn what a really good performing saw should feel like. I have purchased a lower end saw that was not performing at it’s best but my experience reveled that and allowed me to correct the issues. Veritas tools or other well known brand names shouldn’t have that problem. The saw teeth of Japanese saws can be somewhat fragile and are much more difficult to correct than western saws, They are generally treated as disposable by western woodworkers because of the difficulty with sharpening.
The higher end saws are great but they will cost you about double (and up) what the Veritas saws cost. I have tried several of them out but just couldn’t see the extra money for the difference in the performance. They are beautiful and perform well and you can keep them in mind after you have deeper pockets. You can save a lot of money with the old saws after you learn how to make them perform well and get the necessary tools and skill set.
I have new saws, old saws, saws of several types, Japanese and western saws. The go-to saw I keep at my bench is the Veritas 14 TPI dovetail saw. There are others there and I use them for various functions, but if I had to just have one, the Veritas would be it. It does a fairly good job at cross cutting too. and is big enough for most tenon work. The 20 TPI will give you a slightly better finish but it is slower and doesn’t work well for cuts thicker that about 3/4 inch because the gullets fill up with dust.