第1段： some people hold the opinion that a is superior to b in many ways. others, however, argue that b is much better. personally, i would prefer a because i think a has more advantages.
第2段：there are many reasons why i prefer a. the main reason is that ... another reason is that...(赞同a的原因)
第3段: of course, b also has advantages to some extent... (列出1~2个b的优势)
第4段: but if all these factors are considered, a is much better than b. from what has been discussed above, we may finally draw the conclusion that ...(得出结论)