@alibobo I would first of all seek out a second vet's opinion ! The dog is one year old, and the second testicle has now descended.
How experienced with Basenjis is your vet ? Is he aware they carry fore and aft, not side by side as most breeds do ? So when he claimed the first descent was 'in the wrong place', did he really know what he was talking about ?
If you haven't read the post which quoted Liz McCargo's well reasoned and well expressed reason for NOT neutering a young dog, message me with your email address and I will send it to you.
Although I guess it is in the archives somewhere.
I don't think the difference in size would make any difference but if quality of life deteriorates in old age, you can always castrate him then.
Neutering would indeed save you any responsibility or need to be vigilant during the season season, but you also have to consider what such drastic changes can do for the dog as he matures. Yes, neutering probably makes no difference to a Basenji in the short term as people here are telling you but you never know what could happen much later on.
It is not that difficult to be careful !