I'm in a similar boat, when I head up in June I'll be doing a solo dinner on arrival night, staying at Boardwalk. I'm very familiar with both restaurants and I'm up at Disney a lot being a S. Floridian, so 've well established which restaurants I like the best.
I'll differ from some of the opinions here about Topolino's - it's always been of excellent quality and very enjoyable meals every time I've eaten there (5 times now)...service is excellent, beautiful view, and for me, well worth the price.
Trattoria is fine too - I wouldn't quite put them at the same level of service or food quality as Topolino's but certainly good, and with a more comfortable Italian menu, so it's often been a fallback for me when I either can't get into one of my top favorite spots, or just want a more casual or convenient sit-down meal. There are times I want fancy menus and high-end steaks and such, and times I just want good comfort food (Italian-American food is that for me).
So my first-night reservation in June is booked for Trattoria. And I'm looking forward to it. I can drive up, get my room, unpack, walk over to DHS for a few hours, walk back and have dinner on the Boardwalk, then either head out to Disney Springs, back to DHS before they close, or just back to my room if I'm more tired and relax.
If you like the menu better at Trattoria, no matter how good Topolino's is, it's not worth just eating there for the setting or service and not really enjoying the food selection. Enjoy Trattoria!