The practical difference
Canon PowerShot models often win for beginner setup because many use SD or SDHC cards, and the popular A-series can use AA batteries. Sony Cyber-shot models often win for sleek pocket bodies and a very recognizable compact-camera look, but many older models use Memory Stick Duo / PRO Duo cards. That is not a dealbreaker, but it means you should price the reader and card before buying.
Neither brand is automatically better. A tested Sony with battery, charger, card, and a fresh flash photo beats an untested Canon body. A complete Canon kit with common cards beats a cheap Sony that needs a rare accessory path. Judge the whole setup.
Good Sony Cyber-shot routes
The Sony Cyber-shot DSC-W55 is a 2007 7 MP effective CCD compact with a 38-114 mm equivalent 3x zoom, Memory Stick Duo / PRO Duo storage, and NP-BG1 battery. The Sony Cyber-shot DSC-W120 is a 2008 7 MP CCD model with a 32-128 mm equivalent 4x zoom, Memory Stick Duo / PRO Duo storage, and NP-BG1 battery. These W-series cameras are straightforward pocket options if the card path is handled.
The Sony Cyber-shot DSC-W170 is a 2008 10 MP effective CCD compact with a 28-140 mm equivalent 5x zoom and NP-BG1 battery. The Sony Cyber-shot DSC-T20 is a slimmer 2007 8.1 MP effective CCD camera with a folded 38-114mm equivalent 3x zoom, NP-BD1 battery, and Memory Stick Duo / PRO Duo cards. Choose W-series for a more normal compact shape; choose T-series if the style matters.
If you want more zoom, the Sony Cyber-shot DSC-H20 is a 2009 10.1 MP effective Super HAD CCD camera with a Carl Zeiss 10x zoom, Memory Stick Duo / PRO Duo storage, and NP-BG1 Li-ion battery. It is less pocketable, but it gives more reach.
Good Canon PowerShot routes
The Canon PowerShot SD1000 DIGITAL ELPH is a 2007 7.1 MP effective CCD compact with SDHC / SD / MMC storage and NB-4L battery. The Canon PowerShot A590 IS is a 2008 8.0 MP effective CCD camera with SD/SDHC cards and 2x AA batteries. These are very different bodies: the SD1000 is the pocket pick, while the A590 IS is the safer battery pick.
For a more serious Canon compact, the Canon PowerShot G9 is a 2007 12.1 MP effective camera with a 1/1.7-inch type CCD, SDHC / SD / MMC storage, and NB-2LH battery. The Canon PowerShot S90 is a 2009 10 MP effective compact with a 1/1.7-inch type CCD, SDHC / SD / MMC cards, and NB-6L battery. These cost more, but they offer a more advanced compact feel.
Which should you buy?
Choose Canon if you want the simplest card path, AA battery options, and a huge model family to compare. Choose Sony if you like the Cyber-shot body design, want a T-series or W-series look, and are willing to handle Memory Stick accessories. For either brand, avoid listings with lens errors, missing battery doors, corroded contacts, or no proof that the camera writes photos.
When prices are close, let the accessories break the tie. A Sony listing that includes a working battery, charger, Memory Stick, and reader may be a better buy than a bare Canon body. A Canon listing with SD card, charger, and a fresh flash test may be safer than a prettier Sony with missing parts. The brand decision is really a complete-kit decision.
Before buying, read the used camera checklist. If you are not sure how the cards work, read the memory card article. If your goal is easy phone posting, the photo transfer guide may decide the brand for you.
If you still cannot decide, choose the listing with better proof. A short video of the lens opening, flash firing, and image playback is more valuable than a famous model name. These cameras are old enough that condition beats brand in many real purchases.
Sony Cyber-shot DSC-W55: a 2007 CCD compact with Memory Stick Duo / PRO Duo storage and NP-BG1 battery.
Next step: compare the Sony W55 with the Canon SD1000, then choose based on card reader, battery, and listing proof.