Rob - This may be a little subjective /w3tcompact/icons/grin.gif.
We're replacing our 37 year-old wood double hungs and aluminum storms on the North (back) side with Pella Prolines. As you know, they are aluminum clad wood. We're using them because it's what my Dad used in his house, and what he mostly installed in other houses he built. He never liked Anderson because Grossman's sold them and he always thought they were consummate Dubs, plus some of the Andersons were real "budget" products (especially in his favorite store). His real opinion is that Anderson and Pella may now be similar, but he liked Pella 'way back because of the quality, and they had retail stores locally where he could always get replacement parts. Marvin is apparently the "Cadillac" - I don't have experience with them, but am learning they are really good. Pella has a couple higher priced architectural lines, too, that may compete with Marvin.
Caution - Rant Zone Ahead - Prepare to Diverge!
Pella used to be in Home Depot but are now not. I take that as a plus for Pella; I'm developing the same opinion about HD as Dad had about Grossman's, for anything other than small parts & pieces here and there. I bought HD's better insulated vinyl storm doors last year and am happy with them so far. On this rebuild/re-insulate/reside/replace windows project, HD struck out badly, having no Pellas, and very few other things I was looking for, including a decent hammer type stapler. For large projects, I'm going back to real lumber yards. Our local yard beats their prices, they have Pella products, and the experienced sales people are there. Do yourself a favor and compare the quality of various things from plywood to drip edge and flashing with local yards before you order up a ton of stuff at HD. I've seen significant differences in what you would think were "standard" building products, enough to bother me about the windows. I had a brief, exciting fling with HD, but I'm back to the less exotic but more dependable partner, now. If anyone can correct me, I'm all ears (well, there's actually quite a bit of gut, too).
Rant Zone Ended. Resume Speed. /w3tcompact/icons/eyes.gif
The thing I would mention about new windows, at least the Pellas, is that the exterior appearance has changed. There is a thin aluminum nailing flange on the exterior instead of the wider, brickmold type wood molding/nailing flange. There is now only a narrow exterior frame exposed, and it changes the proportion and appearance of the trimmed area of the window. Some people install additional trim (~2" stock) around the window to fill out the proportions of the window. Compare older windows to newer ones and you'll see what I mean - the newer ones look more modern with their narrow lines. You may like it, but you may be unpleasantly surprised at the change it makes in the appearance of your house. We are now deciding whether to fill it out and paint it trim color. We also ordered the windows in tan to try to compliment the light color of the trim, as we found white was too stark. The screens in the same tan color, too.
We found that the rough openings on our house were a bit narrow for the available window sizes. We definitely didn't want to drop down 2"- 4" in width, and shoehorning windows into place is a bad idea - they won't work when the framing moves due to climatic changes. We simply zipped out one of the 2x4 jacks and replaced it with a rough 1" board - being careful to note what that did to the interior location of the window before deciding which one the cut. A rough or full dimension board is plenty strong, nailed to the adjacent stud, and we could use the larger windows. We also "padded" up the bottom with rough boards, as there was plenty of height in the original framing, even with the old windows. I would highly suggest getting exact rough opening measurements - even if you have to remove interior molding to do so - before you pick up your windows. You need about 3/4" over the window size, which will be spelled out by the salesman or in the manufacturer's info. I suppose I need to say you should talk to a contractor, but I wouldn't be afraid of cheating like we did on the framing - assuming you have good, properly-framed openings.
We'll be replacing the rest of the windows as we move around the house and re-side using clapboards (still think vinyl is a passing fad /w3tcompact/icons/smile.gif, like smokless powder, the automobile, and computers). We may check into the Marvins or the other Pella lines for the front, just for fun. Keep in touch on this.