If you're going to be upgrading gear then you might as well just buy Vanguard/Crucible/Faction gear that fit your play style (more ammo for scout rifle/faster reload for scout rifle for example). Ascendant shards are only useful for VoG raid gear and new legendary gear. You'll still be earning them so you might as well upgrade something. You only have two chances per week to get VoG gear you want. That's a minimum of 4 hours of playtime with no guaranteed result vs. putting the same time into bounties and strikes to earn rep and marks to buy what you need with the added bonus of going to 31, not 30. I'm 30 and still bought new gear since I'm turning in bounties anyway so why not equip new stuff instead of wasting the xp on just guns. Plus I was storing too many marks and spending them. That's pointless too.

Buy from vendor. And run vog. Vog is for exotic weapon and exotic gear and vendor is for legendary gear which will take you to level 31 while vog legendaries will only get you to 30.

VoG gear can only max you to lvl 30 so technically the vendor armor is better since it maxes you to lvl 31. The purpose of getting past lvl 30 is to be able to go into the new raid and hunt for the equipment to get to lvl 32. So at this point i suggest that you equip your exotic gloves, your raid chest and purchase the vendor boots. Eventually you should look to replace your helm with an exotic helm and replace your gloves with the vendor gloves. it's on to the new raid after that.