Fishless cycle is kinder on fish as you arent putting fish in until the aquarium is cycled. You can also fully stock your tank quicker than with a fish in cycle. Normally takes 4 or 5 weeks and you can pretty much fully stock.
Fish in cycle gets some fish in the aquarium straight away but you have to add in more fish gradually as the beneficial bacteria grows to colonise the filter and might be 2 or 3 minths before you are fully stocked. Some people see it as an inhumane way of cycling as the fish have to live in uncycled conditions. It also involves a lot of water changes.
Its up to you really. Depends on your priorities and sensibilities. Do a little research on both and see what is best for yourself.
If you go fish in, start with 1 small fish per 10 gallons.
If you go fishless, you will need an ammonia source to replicate the fish waste. Either pure ammonia, ammonium chloride (i use a product by Dr Tim) or fishfood.