OmAziz

I liked Magoosh for verbal, and I wish I'd known about it earlier. I studied all of their more common words, and all of Kaplan's 500. I relied solely on Kaplan for quant and AW. And I did ETS an powerprep exam.
I took a Kaplan course- tbh, most of the material was in the book, so the class wasn't strictly necessary to get the info, but it was great for me and kept me motivated. To me the best perk was that they let me do a mock exam at my testing center through Kaplan, and look at the results at home. I got invaluable advice from Kaplan about strategy- for all of the sections, but esp verbal and AW. That alone bumped up my score by a lot. Overall, I think Kaplan's prep is tougher than the real deal, but it makes you super prepared! And it's somewhat adaptive. So I do recommend them, if you want a class. Their online recorded classes that you can watch are pretty good too.
It seems great to use ETS. Just make sure to consider whether the exams are adaptive at all- their online powerprep is not. Remember, everything will get harder if you do well on the first exam!! I think it really helps take an online adaptive exam at some point in your prep, so you know what it feels like.
My main tips:
1) Verbal: Know the vocab. Be able to answer the question FAST so you have extra time for reading comp questions. I really recommend finding mnemonics or silly associations for each word, or, if you can't, read about its etymology and practice using it (anything that makes you spend a few minutes with the word is more helpful than getting it wrong five times with flash cards, IMO).Anyway, know them well, and don't spent too much time on vocab questions! Read the question without looking at the answers initially, and try to fill in a simple word in your head. E.g., if the sentence says something like, "She was usually talkative, but today, she seemed ___" you should immediately think "not talkative". Then, a word like "laconic" will pop right out at you--and you won't get bogged down trying to think about whether "enervated" also makes sense in context. And always re-read with the words quickly to make sure you picked right. As for reading comp, the answers are always in the text, so it's all a matter of time to pour over the details. The more time you have, the better you'll do.
2) Quant: I don't like math, so for me this was a confidence game. There are strategies- know your pythagorean triples, eliminate strategically, work backwards, etc.- you'll find them everywhere. My main tip if you're also not a math-person is to skip questions if you're not going to get it fast. Mark them, and come back to them later! Each question is worth the same- and you can review all your answers later easily. Make sure you get the easy questions. It really helped me feel confident about the tough one's I'd skipped to get to them at the end with extra time and a lot of easy questions already solved. Also, make sure to practice a LOT of different kinds of questions.
3) AW: Any guide will tell you this- but for the issue, pick your side, and for the analyze an argument one, don't! I think some basic essay advice is solid here- spend 5-10 min on prep, and do a quick outline so you know where you're going. Do all the nice touches- open each paragraph with a nice transitional word, and make it easy for them to see structure. Your conclusion matters more than another body paragraph does! The grader will give you 2 minutes of his or her time. Make it easy for them to give you that high score. It's all about structure!
Good luck!