if you   coin the portals  its  300 in bounty

mountains  you can get  tokens for  in bounty  honestly  the mountains quicker to get done but some people dont like them at all 

moutains are not need to  stop the  wars and  trenchers and they dont  stop hellswarms at all  the portals will  allow you to kill  upgraded  wars and  kill badly build  trenchers they wont stop  the  upgraded swarms unless the  player is  a bad driver or built his ships badly.

 if you  lay your  newer composite walls out where they  two rows of them it will stop most players from trying to blast thru them to kill  something  thats behind them   

 just remember if you  build  mountains to check  and see which base defense weapons fire  over them. some of them dont and it allows the attacker to  hide be hind them..

i would  do  4  mountains first then   go with the portals 
 if your a  light or medium coiner i would  look at one of the gold sales   54 days for  3 portals to  lvl 4 is   a long time thats  if  your not getting attacked  while your tryng to build them if your active hitter its probably more like 80 days for them to  build.  ..... mountains  take 11 days   but they dont get any build time stoppish  because they dont get damaged. my 2 cents would be coin the portals and  slow build  the moutains.

In the end I decided on portals because I remembered from the last outpost upgrade that upgrading the outpost was locked behind upgrade levels of base buildings, structures, portals, etc. There's less chance of next outpost upgrade being locked for unbuilt mountains.. and a higher chance they would require max lvl portals.

Paul Larkin said:

In the end I decided on portals because I remembered from the last outpost upgrade that upgrading the outpost was locked behind upgrade levels of base buildings, structures, portals, etc. There's less chance of next outpost upgrade being locked for unbuilt mountains.. and a higher chance they would require max lvl portals.

That doesn't sound right to me. Portals have never been a prerequisite for upgrading anything that I'm aware of. There's no practical advantage of level 4 portals over level 3, but it will always be a stepping stone to level 5 which may add some really functionality advantages. In other words, something to consider, but not a priority until there's a real reason to upgrade beyond level 3.