I was wondering what would the better Beocord, 4705 with 3 heads or the 4715 with 2 heads.

It's not a question about how troublesome they are but if there is any advance to buy any of them as I have an option for buying either one.

The 4705 is very difficult to get working properly and the three head design was tricky to set up. The 4715 has the same basic mechanism - the only full B&O design - but is more likely to actually work. The 4705 is rarer so if collecting, it is the original one, but I wouldn't put a tape near it that you value!

The best cassette deck made by B&O is the 8004 - reliable and superb performance.