We bought the Alpha Omega Elite by Cosco (not the warehouse store) and have used it for 6 years. My daughter is 7 and still in the same car seat (tiny girl and over protective mom). It's a pain to take apart and clean (straps loop through here, over that, under this, between those, etc.), but it wipes up beautifully. You wouldn't know it was over a year old.
It also converts to a booster. The back adjusts up and down to put the shoulder strap at just the right height. Additionally it has these side wings, which make great head rests, even for 7 1/2 year olds who still take naps on the way home from school.
It was EXPENSIVE, but we bought one for each of the three cars.
As for strollers, we had that big ol'Greco. In all honesty, we JUST got rid of it last summer. While bulky, it was great for hauling things. Even though my daughter wasn't in the stroller anymore, we took it shopping to carry bags, for her to rest (marathon holiday shopping), and used it in the garden to carry bags of soil amendment and fertilizer. We used to to carry the neighbor's dog, who gets tired before the other dog, so she rides home. My daughter also under it to take her babies for rides. All of them could fit inside at once (Well, she did put quite a few in the bag carrying zone.) I say, it's sturdy and will be around for a long time. Besides, it will build your muscles every times you load and unload the thing.
Stephanie