Well it really depends what your play style is in a MOBA.
If you are going by pure value? Mega Bundle Values in descending order Gold
Assassin: 145000
Tank: 141000
Support: 131000
Flex: 123000 Shards
Assassin: 18200
Tank: 17000
Support: 15200
Flex: 14000
Description of Mega Bundles
Assassin
The Assassin Mega Bundle is hyper-focused on Heroes who dish out destruction wherever they go. Get in your opponents' faces as a sustained auto-attacker, nuke enemies from the back line, or roam the battlefield to gank unsuspecting foes.
Flex
If you’re eager to fill gaps in your team comp, or are brand new to MOBAs, consider picking up this bundle to gain experience with a wide variety of roles and playstyles. Includes Warrior, Specialist, Support, and Assassin Heroes.
Support & Specialists
Play-makers in Heroes of the Storm come in many forms. The Support & Specialist bundle is all about keeping your team in fighting shape, turning the tide of battle, and providing the flexibility and strategic tools to conquer any obstacle.
Tanks & Bruisers
This bundle is brimming with Heroes who have no problem getting up close and personal with their foes. Create opportunities to pick off an enemy, peel threats away from your teammates, and lead from the front with the Tanks & Bruisers bundle.
I went with assassins because I generally play tanks and bulky characters, for once I wanted to be a carry or do some serious killing. Flex is usually what to recommend as it has a bit of every type.