I happened to take AZ Magnifica FCO to BOS this month and can compare to DL BE 767 lie flat.

Seats:
AZ is definitely better. There's so much more space including a much bigger footwell. You don't feel cramped into a small space like DL. The AZ screen is larger as well as the tray table. There's more storage space (although there's no overhead space above the middle seats) around the seat. There wasn't any problem getting space in the overhead bins above the window seats.
The center seats come in "honeymoon" configuration and "non honeymoon" configuration. I would not hesitate to take a non honeymoon center seat if travelling alone; the two seats are far apart.
All row 1 seats have some extra space in front of their screen (a ledge). You could use this to store the pillow and blanket.
AZ uses a 3 prong headset. I don't know if you can use a two prong headset.
There were about 12 empty seats so AZ protects the integrity of their business class.

Food: I'd give the advantage to AZ but I can see that it can be a matter of opinion.
Bread: AZ is so much better if you want a crusty roll with a nice doughy inside. DL is totally incapable of providing anything like this.
I liked the cart service: you can see what you're getting and you pick what you want and how much you want. I'm looking forward to DL's implementation of cart service.
Lunch Menu:
Appetizer
Zibello culatello with quice jam and mixed vegetables
Smoked salmon herbs tartare
Parmigianno Reggiano flan with mushroom ragout
First course
Large herbs filled dumplings with béchamel sauce
Pasta with San Marzano tomatoes and basil
Entrees
Parma rose-like meat roll with Marsala, Lambrusco and rosemary sauce
Romagna fish roll in corn crust with mint courgettes
Sides
Buttered spinach
Breadcrumb tomatoes
Sautéed potatoes
Green salad
Bread
Rosemay topped bread
Wholemeal bread
Walnut bread roll
Spighetta baguette
Desserts
Vanilla flavored butter mousse with amaretti and biscuits
Maria Luigia cake
Fresh seasonal fruit
Espresso coffee and tea
I enjoyed all of the food except for the fish roll which I didn't find particularly great.

Service: DL is better.
Preflight: DL FA are there to greet you quickly, get your drink order, get your jacket, pass our menus and newspapers. On AZ, they do pass out drinks and newspapers but not as promptly, nor as eagerly/service oriented way (hard to describe). On AZ, I had to hang my jacket next to my IFE screen (there's a hook); finally, in flight, an attendant offered to take it.
In flight: DL does a much better job making sure you always have a bottle of water, starting with preflight and regularly throughout the flight. AZ FA only come around occasionally.

Lounge (Le Navi, specifically): DL better
I thought that SkyClubs were bad, but Le Novi was the worst. No air conditioning (really hot), sparse seating, crowded, an uninterested bartender, a couple of pastries for food. I understand that AZ has better lounges but Le Navi was the closest to our gate.