If you can afford a nanny then I think they are the best option for an 8 month old, followed by childminder, followed by nursery. Whatever a nursery may tell you, children don’t actually start to benefit from the socialisation aspects until around the age of 2 at the earliest.
Before then, the best thing for your child is a secure attachment with one person (which they are meant to have with their nursery keyworker but it’s obviously much harder in that environment). Benefit of a nanny over childminder is that your child will be in your own home, you can dictate exactly what they do (choose activities etc), and your baby will have one to one attention (whereas childminder will have other kids and will have to do eg school pick ups and drop offs). Nannies also make food and can do light housework like cleaning up after meals and the baby’s laundry. You also don’t have to worry about pick up or drop off and they’re usually a bit more flexible on timings, plus most offer babysitting (for overtime pay obviously) so you can have evenings out too.
Downsides of a nanny are the cost, admin (you have to employ them so responsible for NICs, tax, playslips etc, though you can outsource all this to specialist companies), and you have to agree holidays with them.
With both nanny and childminder you’re at their mercy if they take sick days, but the flip side is that a nanny can look after your child when the child is sick (likely to be much more frequent than the nanny being sick), whereas nurseries won’t let you bring your child in. Especially at the beginning when their immune systems are still developing they might be off nursery sick more than they’re actually there, and you’d have to take annual leave to cover that (unless family can step in).