The 60's era Bonnevilles are the most sought after with the 1969 being the Holy Grail of the Bonneville line. Now that these 60's models are becoming scarce, the 70's and up are becoming more popular. Folks were avoiding the OIF models; but now those are about all that are left.
Actually, 1970 was the most desirable year for the Bonnies. That was the last year of the true Triumph framed bikes, and had all the benefits of the tweaks and improvments. The OIF's started in 1971, 71 and 72 being the "Bad" years of too tall bikes, and engines that wouldn't fit without the heads removed. They got better after 1972.