From the chic France form to the sophisticated Star form, there's a Furfrou for every fashion forward trainer. When it comes to battling prowess, Furfrou's forms don't alter its stats.
Pharoah is easily the rarest trim.
Currently Furfrou forms are only obtainable in Gen VI and VII games, but any Furfrou put into Bank is immediately reverted to natural form. The only way to get Furfrou in Home with any other form is to transfer it from GO, but Heart Trim specifically is currently unavailable in GO.
Evolutions. This Pokémon does not evolve.
Furfrou is a highly valued Pokémon and especially sought after in Pokémon HOME. It is very common to see users willing to trade Legendary Pokémon and Shinys for a Furfrou with hard-to-get trims like Pharoah. These styles can only be obtained by using the Change Form option within the Pokémon's details menu.
You can't change it's form after transferring it, so yes, change it before you transfer it. Heart Shiny Furfrou is one of the rarest but if you have Pharaoh or LA Rein, you might consider them too. I imagine the Heart form will go away after Valentines Day like it did last year.
Pharoah Trim is obviously the best choice for Furfrou, sporting an outstandingly regal cut that brings out its royal blood. Pairing this form with Cofagrigus is a must.
Which is the best Furfrou form? Furfrou's forms are only an aesthetic change with no impact on stats or gameplay. That means you can pick whichever Trim you prefer since none will put you at an actual advantage or disadvantage.
Pharoah is easily the rarest trim.