Need some advice...

Can't speak to the choices named above but I loved Casa Cristina. Ashanti's Place (run by the daughter of Casa Cristina's owner) looks nice, too.

Congratulations!

Posada Burkhardt was really pretty. Tastefully decorated in Guatemalan textiles, lovely hardwood furnishings, and green plants/trees in the courtyard-like setting. It was about 100-150Q per night. Priavte room and private bath. They book up quickly. Unfortuately, we were not able to get a room there, but some friends did.

They are listed in some guidebooks - I think Rough Guide.

Hopefully one of the many local TT posters will be able to provide more accurate details than myself!

Antigua was one of the few places it would have been nice to have reservations. We found a decent place, but only after driving around and around on the cobblestone streets and checking out about a half dozen hotels. It became annoying. We had to stop and spray WD40 on the leaf springs because it was so noisy. Parking was somewhere down the block and the guard, who promised to open the lot at 6am, didn't show untill about 10.

Posada San Pedro is an excellent value. There are two of them, one a few blocks northwest of the parque, one a few blocks southeast. I think the one northwest would suit you better.

Buen viaje!

Those are all nice places, and there are many more nice hotels in Antigua just depending on your budget. I would recommend reserving 1 night somewhere and then walking around the next day and maybe choosing somewhere else if you feel like it.
If you do decide to get out of town for a day or two, the Earth Lodge has an amazing tree house that is super romantic. the owners told us that people have gotten engaged in there, and sometimes they do weddings as well. A Small, cute place and worth checking out...it is only 20 minutes outside of town and if you like nature and hiking and do something a bit different that is not a typical hotel/hostel it is a great place. earthlodgeguatemala.com
Good luck!