Link gets screwed by marth's grabs, link can't defend himself very well at all in the air if you space well.
If the link isn't sweetspotting well, counter his up-b...I've seen too many marths try to f-smash a link that doesn't sweetspot and get caught up in the attack, just dumb.
If you are double fairing or spacing good, those projectiles shouldn't be hitting you unless you are charging him too fast..take your time in your approaches and slowly cut down the distance, hes bound to try to turn the tables and assault you during this so just be wary.
Link does NOT counter marth at all in high level play, hes not an easy matchup as the other low tiers, but countering him? very very wrong.