Hi,
There are a few issues to take into consideration when you are having twins. When you have healthy, full term twins, then a breastpump can be just obsolete. When you are feeding twins there is little time or energy for pumping. However, twins are more likely to be born premature, and this brings it's own set of issues. If your twins are born early, then you are best to use a hospital grad rental pump - these can be rented from the Australian Breastfeeding Association. The support ABA offers is invaluable.
If your pump is for occasional feeds one of the less expensive electrics ie a medela swing might be adequate. (But it wouldn't be for expressing for prem twins who are unable to feed at the breast) I would stick with a medela or possibly Ameda brand. But I would consider just holding tight for the moment and assessing your needs when your babies are born.