ECDHE_RSA_WITH_AES_128_GCM_SHA256 is the cipher that corresponds to "TLS 1.2, RSA with ephemeral Elliptic Curve Diffie-Hellman, AES with 128-bit key in GCM mode, AEAD".
RSA_WITH_AES_128_GCM_SHA256 is very similar, but uses RSA instead of Elliptic Curve Diffie Hellman for key exchange (see the list of supported ciphers).
TlsCipherSuite.All should not take longer time to negotiate - the TLS server chooses a single cipher each time and there is no additional overhead. If might be interesting to try connecting with
ECDHE_RSA_WITH_AES_128_GCM_SHA256 to see whether it takes longer as well (in general, ECDH key exchange should be actually be faster that RSA key exchange).