vanitygen parameter "-F" in what format pubkey need?
"pubkey" is already the default. The -F parameter would be used as following:
.exe -F pubkey 1...
.exe -F compressed 1...
.exe -F script 3...
Each bitcoin address is the result of an encoding of a hash the public key. That public key can be expressed in two ways, uncompressed (equivalent to X and Y coordinates) and compressed (equivalent to X coordinate and a sign, from which the Y coordinate can be derived).
Say you generate '1abc' using both (don't actually use these keys/addresses!):
vanitygen.exe -F pubkey 1abc
The private key for an uncompressed form always starts with a 5.
vanitygen.exe -F compressed 1abc
The private key for a compressed form starts with a K or an L.
This is generally how wallet clients etc. recognize which form to use, and that's important because of what I mentioned earlier. Let's say I use the private key 5KG6rY, once with the correct uncompressed public key, and once with an incorrectly assumed compressed public key:
public key (uncompressed): 04C57E907AEC9BA14D377EA1627672197A87D38A0BB12A390B1504FF9A6A941772D052906B5A5AFB908E096C1C884C0E14096BB47EAC617C99DEDADBC4AE5241F7
public key (compressed): 03C57E907AEC9BA14D377EA1627672197A87D38A0BB12A390B1504FF9A6A941772
So you can see that if you make an incorrect assumption, you end up with the alternate (non-vanity) address.
( You'd probably be searching quite a while to find a private key that yields a
vanity prefix in both uncompressed and compressed, let alone the same
As a general rule, you should probably be using "-F compressed", as the blockchain ends up being smaller if everybody used compressed public keys (even if it does get negated by dust, comment spam, tumblers, etc.), but either pubkey or compressed will work.
The "script" one is a parameter you can ignore unless you really want to muck about with BIP13 type transactions
( Note that the above applies to Bitcoin addresses - if you're generating for an altcoin, the -F parameter may or may not apply depending on that coin's details. )