Do what feels best to start with
Outside 3 is good. Mohawk entry is easier with high speed, but make sure you get deep enough edges when doing Flip from the mohawk, as it's easy to go too straight into it (and not get a proper inside edge/curve). Same thing with the outside 3 of course: Don't rush the jump, you need a good inside edge and a curve for a proper Flip.
Back power 3 turn (Rittberger step) into the mohawk is another, perhaps rather advanced option, but it helps with timing and getting those proper edges for the rotation, compared to going straight from forward skating into a mohawk, imo. It's a cool entry for Toe Loop as well.
And if you can do a spread eagle, that's a really good entrance for spicing up that outside 3 entry with stronger edges (Malin often does his quad from it). Spread eagle is also really good going into Axel.
My 2 cents anyway, good luck!
Edit: Oh, and if you just want to build some courage getting speed on the Flip entrance, then split jumps are your friend, regardless of which entrance you go for! Obviously you don't need to go crazy with the split, the idea just being that you get comfy with that faster speed in the entrance, with half a rotation and landing forward, so you feel safer.