I have somewhere I'm going with this but I want to see if my assumption is right.

What species would you convert your characters to and what would you convert from?

Well more than anything I want to get rid of my engineer first.

Was my first character didn't know any better at the time.

For race I am ofc going with alien since you get the most freedom with it, you could say there are a few race specfic bonuses like the gorn bite or thrill "efficient" to consider but I'd much rather have the ability to change my appearance.

I'd respec my Male Pakled Tac into a female joined trill tac.

Orion to Klingon. I'm not sure why i made an Orion in the first place... well, maybe I am; but I didn't intend for it to become my main.

Sadly, if I had an option to swap from KDF to Fed, I probably would at this point. I'm pretty burnt out on getting ignored and marginalized when it comes to them making new ships.

Bolian Male -> Klingon male

i paid for it.. might as well use it

but 2-3 months after that would probably change again..
caitian/bajoran maybe? or possibly alien..

im like that

If they existed, I wouldn't use them.

I've got a bit of alt-itis and generally plan out my characters thematically and playstyle-wise before I make them. Oldschool table-top habit, perhaps.

Same.
I would switch to aliens for any non-thematic characters.
The range of passives and the appearance options sell alien for me.
I almost create nothing else when creating Alts these days.

Human to Liberated Borg Human.

On the contrary to some, I make alts but never ever play them.

I'd only respec one of my KDF characters: from "Alien" to "QuchHa'" (the term used for the TOS Klingons)