I'm told Deerpark offer an excellent service and, as long as you are on UK or Irish mainland, it's maybe the best option. The only reason we don't use them is that we're on a Scottish island and even first class post can take four days to get here.
Of the alternatives, keeping one boar is expensive and not really worth it unless he's going to be working regularly. Keeping more might leave you struggling to make any money from the venture unless you are going to be working on a large scale.
An alternative would be to rent boars from other local breeders. Have a look at the various breed websites. The only trouble with this is moving animals on and off the holding and the consequent paperwork and regulations regarding standstills.
If I were you, I'd go for AI - or start with one breed and work from there.
Hope it goes well.