Well I have been testing it... in Search I seem to be getting about 10k a game, and Ground Wars I got about 9k, Demolition was also 9k, Domination was 8k... I guess they all are really good lol.
groundwar: if you generally get mass kills, this is a good place to go, + you can capture flags on domination which is great xp if you catch a lot of them
domination: slap on mara/lw and grap an smg and run your tushy off and cap flags, good way to get some xp
best way to get xp though is by doing challenges. go through them and look at hwat you need, then go into your fav gametype and try to unlock them.