We have 2 tractors with guidance and get along great with WAAS. Use it on the planter tractor and in beans its great, corn is inconsistent for guess row width. Like others said, for tillage narrow up the implement width by a foot to cover any drift. When you quit for the day you will find that when you go back to the field you will pretty much always have to "nudge" the A-B line over to where you are starting.

I tried out RTK last year and this year and am trying very hard to convince management to buy it for my planting tractor. It's expensive to start off (about $8000 for unlocks/wire harness) but $1200/year subscription for RTK I can save that on fuel costs combining corn alone.