Really depends on what you use your RDM for.

I Use

Tier 1
5/5 Convert, always helpful
5/5 Ice Accuracy (+15 mag.acc)

Tier II
5/5 Slow II (lands on everything I do, not difficult to cap potency on)
5/5 Dia III (I found this spell extremely helpful, especially on Saboteur Dia III.)

The rest I really couldn't use.

Para II, any NM in the last year and a half will be nearly immune to it. Of those that aren't they have a static 50~75% reduction in it's potency, an ES full potency para II will hardly ever proc on newer stuff. Blame SE. Now saying this, when it works, it REALLY works. So if your frequently fighting things that aren't immune / severely resistant to, then cast away.

Phalanx II, I used to have this 3/5 until PLD's got their phalanx to above my Phalanx II. Afterwords I just use accession if I need to put it on other pt members. Otherwise the PLD's just apply their own.

Blind II, Never found this particularly helpful. 10~20% from 135% hit rate still leaves the NM with 110% hit rate (capped at 80). Vs anything big and nasty this spell is utterly useless due to SE's own system.

Bio III, I loath this spell, especially when another RDM casts it and ruins my own saboteur Dia III. For some reason people always feel they need to cast the highest tiered Bio they have. Anyhow at 5/5 with lots of Dark Skill it's ok for very long duration solo fights. Contrary to what people think, this won't actually lower damage taken due to the way SE treats monsters attack.