There are many choices to consider: As the top 3 noted, these are the most useful for people with NO uridium formations:
Diamond:
I recommend you get this if you are into cubing(with aegis) OR are not able to kill BK without a lot of effort. If primarily fly goli and can pop a bl with the majority of your heal and some shields left, diamond will only have marginal benefits when running around pvp'ing
Heart:
This is a big must. Whether there is a 5% dmg reduction seems trifle. Having 20% more hp and 10% more shield, whether you choose to npc (bk,etc.) or pvp, it will be invaluable. I would say this is the one you should get first.
Moth:
Realistically, this won't be useful unless you are FE and 30-40% ufe. Unless you are into doing a lot of gates (which arguably isn't worth the 100k uri you will spend), this will only help in pvp's where you are able to do some damage. If you can't do at least 40k with x4 and sep, you should wait on getting this design.
Pincer:
Once again, you must have some firepower to use this formation effectively. Simply doing 20k whites isn't going to give you much of a boost.
Please note that all these are opinions that I've formed through constant usage of the various formations. It would be wise to maybe not spend that extra uri on pincer or moth, and possibly focus on apis and zeus if you haven't gotten them already and upgrades.
best of luck
