Good familiars for a Witch with Synergist Archetype?

[Zorajin]

So I'm considering playing a synergist witch and I'm looking at familiars.

I was thinking, to make it really worthwhile to be a Synergist, you shouldn't just use the hybrid form to keep your familiar safe from harm but also gain something like senses, movement types or other useful abilities.

Currently I'm lvl 2 and have already started playing the character as a normal witch with a Greensting Scorpion, but am allowed to make changes between first and second session. So I was considering something like a bat or an improved familiar along with Synergist. The campaign we're playing is Hell's Vengeance so the char is Lawful Evil for selecting improved familiars. I have been looking at getting a Sin Seeker but don't really like the idea of merging with a blind flying pig and halfly becoming one, but I am still considering it.

Any advice from someone who knows their way around familiars would be really appreciated! Even if they aren't available to a Lawful Evil character, it would still be interesting to hear suggestions.

[MageHunter]

Imps get commune which is handy. Plus, they'll just subtly corrupt you. Imo Consulars (see bestiary entry) get cool SLAs.

Homunculi are pretry cool if you've got the cash.

[Zorajin]

Imp seems kinda cool, and I'm lawful evil already so it might fit. I don't like the comment that imps tend to want to get their masters dead though. I kinda wish it had more senses to convey through Synergist archetype to the hybrid form though. Darkvision is nice, but Ioun Wyrd and Sin Seeker both have blindsight for example.

I haven't found any, but isn't there any familiar that has 3 or more of: Blindsight, Darkvision, Scent, Fly, Climb, Burrow, Swim.

It'd become a contender for sure.

[DeathlessOne]

Ioun Wyrds have flight and blindsight 30ft.