Low Frequency vs High Frequency
Low frequency readers are often cheaper (although not always due to the mass production of high frequency).
Low frequency writable tags typically have smaller memory and the data transfer between read and tag is slower due to the lower frequency.
High frequency tags can often have a shorter range than low frequency.
High frequency tags are often cheaper due to mass production volumes.
Maximum range – for low cost modules such as those from people like ibtechnology.co.uk
For high frequency 13.56MHz iCode will likely give you the best range for a writable tag. However it won't be as big as for the best low frequency tags,
For low Frequency 125kHz Hitag 1 will likely give you the best range for a writable tag. This will be better than iCode and has better noise immunity in more industrial environments.
UHF for longer range with passive tags
UHF passive tags can provide reasonably long read ranges (2m for instance) and the ability to read multiple tags all coming into range at the same time, but there are some considerations. The read range it is not guaranteed as the reading of the tags can be easily interfered with:
Firstly the human body is very good at blocking the signal and any tags very close to the skin or on the other side of the body to the reader can stop it working even at 1m range. One solution often used to the close to the skin issue is to use foam between the skin and the tag (>5mm works well apparently), but being on the other side of the body as it passes the reader may still be an issue. Locating tags in a helmet or in the collar of a jacket can be a good way of solving this issue if its possible.
Secondly metal will affect the read range, specifically metal around the reader and metal around / near the RFID tag.
Also important to consider is that UHF readers can be expensive and are not necessarily available with UART interfaces (Ethernet is a popular interface).
Low Frequency 125kHz
EM4100
EM4102
Very popular for read only RFID tags
EM4105
EM4150
EM4200
Very popular for read only RFID tags
EM4350
EM4450
FDX-B
HID Prox
Hitag 1, 2
Hitag 1 gives good range and has good noise immunity in more industrial type environments.
Hitag 1 S256 has 256 writable bits (8 characters). Hitag 1 S2048 has 2048 writable bits (256 characters)
Hitag S
Indala
Flexpass
MIRO
Q5
T5557
T5567
T5577
Ttitan
Unique
Read / Write. Good general use choice.
Zoodiac
Low Frequency 134.2kHz
64Bit R/O
64Bit R/W
1088Bit Multipage
High Frequency 13.56MHz
ISO14443A
Mifare
Mifare general notes:
RFID tags / cards are quite cheap as Mifare is widely used and therefore very mass produced.
Security is available and Mifare is used for London Oyster cards for example
The range of Mifare is not as good as a protocol like ICode (which can give double the range for the same power and antenna)
Mifare Mini, Classic 1k, 4k
Mifare DESFire EV1
Mifare Mini
Mifare Plus S, X
Mifare Pro X
Mifare SmartMX
Mifare Ultralight
Mifare Ultralight is fairly ubiquitous and therefore a good high frequency choice in terms of availability of a wide range of readers and tags.
Mifare Ultralight C
SLE44R35
SLE66Rxx
my-d move
ISO14443B
Calypso
CEPAS
Moneo
Legic Advant
SRI512
SRT512 SRI4K
SRIX4K
ISO15693
EM4033
EM4233
EM4135
ICODE SLI
Very good range. Can be double that of Mifare for a given power and antenna size.
M24LR16/64
my-d
MB89R118/119
Tag-it
HID iClass
PayPass
Legic Advant
PicoPass