Valk is Amazing She can only be pulled from the rare machine, but can basically steam roll a ton of stuff and just make the game so much faster (some bosses when you first hit them can seriously be tankable but you don't have the attack and can take 2-3hours, but valk can speed the fuck out of that). The only issue is you are going to want every healer, which they are not common drops. If the game is getting slow with her in the lead feel free to bench her, basically if you don't have all the healers on your team she's rather weak feeling.
Basically once you get her up and running and have a valk friend you have 6x damage and a bunch of healers to just spam heal yourself to full, oh and succubus will be poisoning the enemies making things nice and quick. If your Valk is 30, she'll really help carry you, if she's low leveled, you are probably going to want to sink your early XP into another good rare pull to make the early game easy.
Most of the recommended pulls honestly aren't that great early game, but are amazing late game, many of the good early game monsters you will not want to use late game anyways, and are more common, honestly the bulk of a standard team is probably going to be dragons and other easy to get to drop things, so you can just main one of them if you really need to. Hell use your starter, you wont get the most PAL points, but PAL pulls are trash. The starter is actually really really good.
Really Valk is awesome and will help you get by so many areas that suck, but what makes her good are the harder to obtain healers, so she will seam weak at first when playing, and she kinda is without the healers. So don't feel disappointed, she really will make the game fucking awesome after a week two. (and you will be playing this game for months).