Hello Aspirant,

Both of these books have their separate advantages.

Plinth to Paramount :-

Good for grammar rules and practice questions of a particular chapter such as noun, pronoun etc.

Good for previous year OWS, Idioms & Phrases, Synonyms, Antonyms, fill in the blanks etc.

Volume I of this book is especially designed for SSC candidates so a lot to learn from this however, volume II is not of that much use.

General English by SP Bakshi :-

Contains a good amount of word apart from grammar rules. If you are done with previous year questions and are looking for to do something that most of the people don't then mug up all the words that published in this book. Especially the additional word provided in the end of the word portion.

Learn narration and voice from this book only, you will, at times, get confused because of the special examples mentioned but it is worth reading.

There are a lot of questions to practice so it keeps getting better.

Good collection of Phrasal Verbs and provided with one or two examples which makes your learning easier.

OWS and Idioms are of previous years you can skip if you don't have time.

Remember, Plinth to Paramount is especially designed for SSC while General English By SP Bakshi is for many others so you get some new questions to learn from.