What is the best way for my husband to enter the country?

Hi, I met my husband in 2011 via a language exchange program; he was in his country and I was in the US. We studied online for a year and interest grew so we decided to meet. He applied for a visa in 2012 and was granted a B2 or B1 (not sure which) He visited the US for the first time ever in 2012 and the rest is history! We married in 2014 in Maryland,US and my husband still lives in his country. We initially had hopes of me moving to his country, but because of the housing situation here in the US, selling our home (that I purchased before meeting him) has not been likely so I can't move. Since 2012, he has traveled to the US 4 times (never overstayed) and I've been to his country twice. We want to be together. What is the best, quickest and most legal course of action? Should I file the I 130 while he's still in his country or should he come here and we file all the paperwork at once? Would that be considered unlawful intent? If he comes to the US, should we file the paperwork right away or wait awhile? Thanks for your help!