I own a number of both Enfields and M39's, including a #4 (and #4 Mk2). Their aesthetic is very similar. Though I find it difficult to call a military rifle ugly, I find that folks generally make their mind up which rifle they prefer, and then look at the others out there and decide what features they do not like (rather than the other way around). Because the Mosin is generally equally as accurate and durable, more durable than many, the critical opinion must focus on the safety or aesthetics.
Ian Hogg has written many, many books on military small arms. He is a British author who has an understandable preference for all things British and certainly does not care all that much for the Mosin.
Me, I like Finnish Mosins because of their historical value and their accuracy. I prefer shooting my Garand most, as it is my most accuract long arm. That said, I have between 1,000 and 5,000 rounds of 7.62x54R, older Russian fare on chargers, some 400 rounds of Bulgarian from the 1980's, a smattering of Chinese, Hungarian, and Czech (and a small amount of East German target stuff) plus a bunch of Albanian.
Ash