My 6 month F visa expires next month, I've had friends go to Hong Kong and get rejected

My 6 month F visa expires next month, I've had friends go to Hong Kong and get rejected even tourist visas. I have a company that will give me an invite letter, and I was thinking of going to Philippines/Mongolia/South Korea to apply for a new F visa. Which close\bordering country has the least restrictions? I don't want to get given a 30 day visa, or even worse, get rejected. I heard Mongolia is very relaxed but the rules are changing every day. I am a British citizen. Thanks.