I use boar and synthetic and I would say they're not easier or harder to lather from one another they're simply different.
They have their own little quirks, for instance boar likes to be soaked for a little bit to soften up before you lather it. Synthetic is ready to go right out of the gate but the synthetic bristles don't retain water like natural boar/badger bristles do.
Out of the two types I greatly prefer synthetic, but I still like my boar.
Something else to note is that natural hair brushes will have an "animal smell" when you first get them, this will lesson greatly as you use them though.
Are you looking to buy a new brush?
Are synthetic bruses easier to lather with than boar?