Highway driving should i buy 4 or 6 cylinder ?

This is your choice. If economy is important buy a smaller car with a 4 cylinder.

Average driver driving normal conditions on typically maintained highways will be fine with a modern 4 cylinder car. A 6 cylinder will be a little less efficient and typically weigh a little more. 180 miles out of your current 4 cylinder is pretty good but don't expect more by buying a 6 cylinder. Taking good care of what you buy and not abusing it by how you drive will do more for you than which engine it is powered by.

4 cylinder, you'll save money. Ive had a 4 cyl and v6 , it costed me $40 to fill my 4 cyl , my v6 is $80 to fill lmao, if you have the money and see a nice car thats a v6 then go right ahead, but over all id recommend a 4

So honda make engine last 180K , i thought 300K , my car only drive highway , it should last more , how come only 180K ????

Perhaps you did not take care of it like you should have.

What went wrong with it that caused you to want to get rid of it at 180K? There is more maintenance required besides oil changes. Timing belt failure, filter changes, ignition part replacements, exhaust components, sensor failures, etc.

too much miles and engine done

It depends on the vehicle your buying. I owned a 2005 Ford Escape with a V6 3.0L, and was always wondering if the base 4 cylinder would net better gas mileage. The best mileage has always been around 20-22 highway. Not to mention that the V6 isn't that much quicker than the four due to the final drive ratio being taller on the V6 vs. the four. Look up the specs for the vehicle.