The closest stays to the moat and Tha Phae Gate water-fight zone are 137 Pillars House Chiangmai and Royal Lanna Hotel, about 470 m and 520 m in a straight line. 137 Pillars is a small 30-room hotel while Royal Lanna has 274 rooms, so choose by group size.
If you stay several days and want to wash wet clothes yourself, Anantara Chiang Mai Serviced Suites is a candidate. Its rooms have a kitchen and washer for longer stays, and an indoor pool and spa make it easy to cool down.
With children, compare Maladee Rendezvous Hotel Chiang Mai and Away Chiang Mai Thapae Resort. Both have a kids pool, and Away adds a playground, a sauna and interconnecting rooms. It is easy to let a child rest after joining the water fights.
For couples, the spa and bicycle rental at Na Nirand Romantic Boutique Resort let you tour the Old City by day and rest in the evening. For a simpler base, POR Thapae Gate lets you move around the Old City on foot.
During Songkran, hotels fill early and minimum stays can open differently from usual. Check the room type and free-cancellation deadline, and consider whether you need cooling facilities in the hottest month of April.