Only Yesterday went from#16 to #44 in One Week !
(12 weeks as of that point on the Top 100 Chart).
In the same issue:
Rock Singles Best Sellers:
#7
What is happening?
That is quite a drop for one week.
In those days the charts were compiled by Billboard conducting a weekly phone poll, where they would call the stores to get their reports of the best sellers. This system has obvious flaws, not the least of which was if a store manager decided he "didn't like" (or "did like") a certain record, he might give that record or worse (or more favorable) report than it really deserved. There were also a lot of instances of store managers "estimating" the sales reports rather than reporting the real numbers. This is why there was such an upheaval when computerized reporting (referred to by Billboard as the SoundScan era) began in the early '90s. So it's possible that "Only Yesterday" was still selling higher than #44 but managers reported that it wasn't doing that well.
Answering the OP question, I am torn between "Close to You" and "Yesterday Once More." Both are perfect Carpenters records and both have that #1 hit potential. I tend to like them pretty much equally as my favorite Carpenters tunes.