I don't think the brand matters too much, those are both good quality brands for breastpumps. Just be sure you get a double electric one if you will be pumping at work. They are the most efficient for both time and milk supply. I had an Ameda, I did like that it had the option of being plugged in or using batteries. Just read the descriptions carefully and see if any features would be particularly useful in your job setting, like a car adapter if you travel for work, etc.
As far as how to get milk supply going....nurse a lot! I would recommend not pumping for the first two weeks and just focusing on nursing your baby on demand, and hopefully very frequently. Many women are concerned about the lack of mature milk at delivery and fear the colostrum available to the baby at birth is not enough. Please try to avoid that fear induced pitfall. Giving your baby bottles in the first few days (or any time really) can diminish milk production. The pump is often not as efficient at stimulating milk as a baby, so only pump when you have to, nurse directly whenever you can. When I worked at a daycare we had a mom that asked us to try avoid feeding her baby after 3pm so she could nurse her right away when she got there, she often nursed right there at the daycare because she had a long drive home. Nurse your baby before work, when you are working pump at least as many times as the baby would be eating, and try to nurse as soon as possible after you pick the baby up, and all evening, and at night. I also tried to pump right after the morning feeding. I was always overfull by morning and had plenty left to pump after my baby had his fill. Also do not try pumping before the baby is born. Stimulation to the breasts like that can bring on powerful contractions, sometimes they are powerful enough to cause stress to the baby. I would encourage you to visit with a lactation consultant at the hospital after your baby is born to discuss your early return to work and get her advice on pumping/bottle feeding for that time. Also, kellymom.com and llli.org are great resources for breastfeeding questions and problems.
I wish you and your baby all the best.