Any time is good for a visit but I always try to avoid the main public holidays, buddhist holidays, elections etc when the bars are shut.
Apart from that the only time I give Thailand the swerve is during Songkran. Loy Krathong doesn't do anything for me...never seen what the fuss was about.
I wouldn't touch Pattaya with a bargepole during Xmas and New Year but staying elsewhere is OK.
