Guardians need low latency to react to and parry attacks. Just keeping a shield up means it'll soon be broken. The best Guardians with low latency I've seen (badworm for example) return every hit they shield.

Going Recon with a big sword is effective, either give your opponents Doom de-buffs (only do that with teammates present) or ambush them with big swords yourself. The Doom debuff will be more important in the coming weeks since everyone will have more health and no defense means your team will actually bring them down faster.

Strikers with swords have the most twitchy reflex based play, and with high latency you might get the first hit (it's calculated client side) but you won't get out of range quick enough to avoid the inevitable counterattack.

Strikers with guns. Gunner-Pulsar spamming is effective almost to the point of being overpowered, just dash a bit between every few shots. It's a supportive action, since you'll deny advances or access to an area. Offensively with teammates, most will focus on the guardian on their point rather than the guy with the cowboy hat dashing back and forth just on the edge of their screen. Shock and hit-flinch effects will give your guardians a MASSIVE advantage though, and usually will get your enemies killed before they see which class the bigger threat is here.

It has the downside that it's very frowned upon, you'll get little respect if you only use pulsar spamming, it being called the "noob" and "no skill" weapon. Also after dying once, people WILL prioritize you after respawning. I'd use it in moderation or when the other team is winning hard, might as well make them fight for their landslide victory ^^

I also make it a point to stop if people say it ruins their fun.