It depends upon what you want. I have spent years on radar, and think most books are not good at all; not that I could write a better one!
Stimson is mainly qualitative. It is written to give you the basic idea, and can be read by someone with at most freshman (college) math/physics background. I have only used it to help me figure out how to explain radar to non-technical types. But I know PhDs that love it. If you want the basic ideas of basic radar explained well and simply ,this is your book. It is NOT my book.
Principles of modern radar is a very good modern book on radar, but requires at least jr/sr level technical background (physics, EE, etc). "Radar principles" by peebles is probably the next best book, but is not as good. These are probably the two best overall books on radar in my opinion.
I am older, so my favorite is "radar principles" by levanon. I took a course out of it so I still look at it quite often, but it is too old to be considered modern (the "processing a coherent pulse train", MTI, and SAR chapters are particularly antiquated). It is thin, which is good, but of course it leaves a lot of stuff out. And the price (particularly the new price, but even the used) is not worth it.
I have finally looked at the radar systems book by Skolnik
https://www.amazon.com/gp/product/0070579091/?tag=pfamazon01-20
only recently. The 2nd edition is certainly worth the $4 US it will cost on amazon.
Enjoy!
jason