I think the entire world would say Funeral was their best album. In fact, you could make a really good argument that Funeral was the album of the decade, and perhaps even an argument that it's Canada's all-time greatest album (though the classic rock folks will disagree, but I think people always tend to favour the older over the newer, whether it's an argument about music, books, hockey players, etc. no matter how good the "newer" is).
To follow up an album like that is impossible to do, but rather than make a Funeral II they took things in a more Springsteen-esque direction, and if Neon Bible was made by any other band it would have been championed far more than it is. The Suburbs is really good though and while it's not a Funeral, there isn't anything that I've heard this year that comes close to it (and a lot of good bands released albums this year, like BSS). I mean, the only criticism I've heard of the album is that it's too long, which is exactly what Win Butler would want to hear since it fits the theme of the album so well. Considering so many bands have released critically acclaimed first albums over the last ten years only to fade away (The STrokes being the most obvious), I think the fact that the Arcade Fire haven't faded, but have only gotten stronger is a testament to how good their two other albums are.