Android has more free apps
Android Has More Free Apps Than iPhone, Researchers Say [App Store Research Firm Distimo Says That Android Market Has More Free Apps Than iPhone, Says That Android Will Eventually Be On Top Of App Store] | TFTS
And 'better apps' and is more welcoming to new apps. iphone chooses what apps to keep and what apps to not even allow. For example they wouldn't allow a Google Voice app (turns your voice into text, saves having to type).
And Google Voice is pretty useful. So I would say Android is the better OS and more liberal with regards to apps.
What you need to consider though is:
The version of Android OS (if the phone has it, not all smartphones do)
Upgradeability
Perhaps technical specs like processor speed, screen size, camera quality, HD video recording etc
Now from what I've read, Samsung make the best quality smartphones. But a lot of them don't use the Android OS! They use their own 'Bada' OS which is seen as bad by a lot of people.
The main issue for me is that the Bada OS does not support the Whatsapp app. Whatsapp is an app available for iphone, android, blackberry and 'symbian' (Nokia OS). It allows free text messaging, picture and video sending, etc.
Notice that Whatsapp is cross-platform. A lot of the good apps are. Some of the better Samsung phones are:
Samsung Wave
Samsung Wave S8500 review from TechRadar UK's expert reviews of Mobile phones
Samsung Galaxy S
Samsung Galaxy S review from TechRadar UK's expert reviews of Mobile phones
Samsung Galaxy S2
Samsung Galaxy S2 review from TechRadar UK's expert reviews of Mobile phones
Note that in the mid-right hand side table, the Galaxy S2 is rated as the top phone, above the iphone 4. iphone 4 is actually in fourth place.
Note: Even though the Galaxy phones have the Bada OS, the Android Market is built in so you can still download all the apps from google such as Whatsapp.
I am looking for a new phone myself and can't seem to find the one I want with all the features I want. The Samsung Wave is technically the best I've seen (price and quality wise) but the fact that it doesn't have access to the Android Market or Android OS is really off putting.
Some other cool apps I had on my last Android phone:
SMS Backup (sends all your text messages to your gmail account. Online backups are great and it does it automatically)
World News
Whatsapp as already said
APN Backup & Restore - automatically sets up your phone for the internet / 3g / mms without you having to manually enter the settings
Can't remember the others, to be honest I didn't use that many but the ones I had came in handy.