As I've said in another thread, there are too many good TF comic covers around to pick a favourite.
My first TF comic purchase was Marvel UK 36 (Dawn of the Devastator). I also liked Marvel UK 42 (Ravage's Resolution: Anarchy in the Ark). My mother decided to rip it up because she thought that TFs were 'too commercial'. I retaliated by ripping up her Which? Magazine holiday supplement! She didn't try anything like that again. Ah, happy days!