I don't really have a favourite. I was very fond of my first tariff.
Vodafone Pay As You Talk (1998-2000)
Top Up - £10
Line Rental - £2.50
Peak Calls - 35p
Off-Peak Calls - 5p
Other Networks - 50p
Off-Peak Hours - 6pm-8am (very generous)
I left because the Virgin tariff was better.
Virgin Mobile (2000-2003)
Top Up - £10
Line Rental - None
Call Charges 15p for 5 minutes, 5p rest of the day
Voicemail - Free
I left after an argument with Virgin customer service. I was overcharged on holiday and they wouldn't do anything about it.
Orange Choose Your Own Off-Peak (2000-2006)
Top Up - £10
Peak - 35p
Off-Peak - 10p
Texts - 10p
Internet - 10p a minute
OR
Top Up - £50
Peak - 25p
Off-Peak - 5p
Texts - 5p
Internet - 10p a minute
+ lunch time off-peak (11am-3pm) something like that
I believe this tariff was discontinued and the £50 discounted call charges became a 10% off instead.
Orange Speak Easy (2006-2008)
Top Up - £10
Call Charges 15p + 15p per hour to 3 Orange users
Texts - 100 free
Internet - 10p per minute / £2 a day?
I switched when texts were upped to 300.
Orange Dolphin (2008-2009)
Top Up - £10
Call Charges 20p + 20p per hour to 5 Orange users
Texts - 100 free (upped to 300 I think from 2009)
Internet - £2 a day (100MB free from 2010)
The internet was far, far too expensive and still is. I kept it as my backup sim up until just last week, when Orange decided to randomly drain all my credit for Internet use I didn't make. So I destroyed the sim card and will never use Orange again.
o2 Simplicity 30 day contract (2009-2010)
Pay - £20
Minutes - 600
Voicemail - Free
Customer Service - Free
Texts - 1200 + inclusive x4 abroad
Picture Messages - count as 4 free texts
Internet - Unlimited
Fantastic, until o2 dropped the Internet deal to 500MB
giffgaff (2010-)
Pay - £10 every 3 months
Minutes - Unlimited to all my friends on giffgaff or 8p
Voicemail - 8p a minute
Texts - Unlimited to all my friends on giffgaff or 4p
Picture Messages - 16p
Internet - Unlimited