The VHII, Abraxas, Crawler and Holy Diver are the most popular choices for alder strats:
VHII - Bright, punchy and clear. The voicing makes light work of pretty much any tone, from classic to contemporary. It'd be a great choice for a session player or cover band guitarist that needs a huge array of tones at their disposal.
Abraxas - A lot hotter than the Mule, but covers very similar ground when used in a Strat. It's rich, open and has a wonderful vocal tone. Capable of a wide range of tones but particularly good at vintage cleans, Marshally crunch tones and liquid smooth solo sounds.
Crawler - More focussed and punchy mids than the Abraxas. It has an old school voicing but is plenty hot enough to cover any contemporary tones. Like the VHII, it's very versatile and would be a good choice for those that need a big palette of sounds, but it has a naturally fatter sound than the VHII.
Holy Diver - A real "silly grin" pickup in a Strat (or superstrat). Much more saturated and compressed than the other three, it's a shred-happy pickup with a very expressive lead tone and tight rhythm sound. It isn't too hot to be able to cover classic tones too, but if those are your priority I would choose one of the others.
