I think you already have the right mindset: With these relatively BOTL TT there probably is not much difference soundwise. But given a choice, I would go for the DD D35 as specs are a bit better, Sansui DD's are quite reliable and Sansui probably put more effort in the DD version as back then DD was a big step up from BD. FYI: I had a FR-D35 once but trashed it as I am not into "plastic" TT's, but to be honest it sounded fine and build quality was not so bad for a "plastic" TT. And I found the earlier Sansui SR-232 and P-50 BOTL "plastic" belt drive TT's not good at all. Reading back these lines, I would definitely not go for a FR-D25 BD.
Any opinions "Audiophiles" have about BD and DD will certainly not have been based on such BOTL TT's as these FR-D's.
As an alternative solution (if available in your country), the belt drive BOTL SR-222 from the mid 70-ies comes in mind. This is a reliable and nice Sansui BOTL TT. The SR-222 MkII version is even nicer (and a bit "quiter"). These TT's perform much above their ranking and are often available for friendly prices.
Have fun
-John-