I actually spent two years as an English major and just recently switched to linguistics.
They're both very interesting fields, but are radically different. Linguistics is more of an empirical field, whereas English is an art. If you enjoy reading literature, English is for you. If you enjoy grammar, Linguistics is for you.
Linguistics departments can very different too. At some schools like MIT and CMU, linguistics is a subfield of philosophy. This means that their department is going to be more geared towards the philosophical applications of linguistics, as the philosophy of language became very hot as the analytical philosophers of the 20th century emerged, killing metaphysics. Other schools have a more disciplined linguistics department, focusing more on grammar and language development. Because linguistics is a rather new and emerging field, universities' programs can be very different. With English, you are going to study the same canonized authors regardless of what school you go to.
To clarify: For a philosophy-oriented linguistics program, you will have to study symbolic language/logic and philosophy of mind and language. In a more traditional linguistics program, you will me studying more psycholinguistics and sociolinguistics.
I switched majors because about 6 months ago I started reading Wittgenstein obsessively and feel that linguistics is the most relevant with the latter part of Wittgenstein's philosophy. However, if I feel it's worth the time, I may try and double-major in philosophy and I almost already have an English minor.