Guns and zombies is my favourite combo (TLS) but my vote goes to Sonny since it's an RPG and also you can play it till you get sick of it, unlike TLS (The Last Stand) you have a limited amount of time (Game must be completed at a pace) so you can't further explore those areas you had to pass.
Last stand 1&2 are good , I like zombie killing games and a taste of gore every now and then , Sonny is a good game however , its a little slow for me , not as fast paced as Last stand , also Sonny is basically just alot of thinking , where as in Last stand you have to shoot alot and find ways to elminate zombies faster , L.S > Sonny