Option 1: "Cambridge English Grammar Language" by Geoffrey Pullum or
Option 2: a site which, i think, is based on government and binding theory: https://www.ling.upenn.edu/~beatrice/syntax-textbook/
if there are better options, please reccommend. thank you.
By invoking "theory", you made the question very difficult to answer, because not only does the work have to account for English, it also has to be a theory. Which aspect is more important?
See p. 18 ff of the Cambridge grammar:
The primary goal of this grammar is to describe the grammatical principles of Present day English rather than to defend or illustrate a theory of grammar.
Compare that to Santorini & Kroch ch. 1:
This book is an introduction to generative grammar from a Chomskyan perspective.
The Cambridge grammar is more a description of English with some assumed theoretical subcurrents, whereas Santorini & Kroch (or, Koeneman & Zeijlstra Introducing syntax) is an introduction to a syntactic theory, exemplified via English. If you are most interested in theory, Santorini & Kroch or, Koeneman & Zeijlstra would be better because that's what those books are about; whereas as a description of Modern English, the Cambridge grammar would be better.
