DS is August birthday. I chose not to send him to pre school at all, he went straight into full time school 2 weeks after his 4th birthday. He did go to creche once a week when I went to a Pilates class and also spent one day a fortnight with a friend and her same age DD, her DD spent the day with us the alternate week.
I think that for him, that was definitely the best choice, he had a speech delay caused by glue ear and I don't think he'd have coped with a large group any sooner. As the pre-school he'd have gone to is in a school, there would have only been 2 adults to care for 28 3 year olds, and I felt he gained more from the time at home with me.
Having said all that, DD2 is 3 in June and will be starting pre school in September. She is a different child altogether, loves being with people, speaks really well and is itching to get into school when I take the older DC.
DD1 is April birthday, and also went to pre-school, 5 mornings a week, from the September after she was 3.
Horses for courses I suppose, and it depends how flexible you can be on the no.of days they go. There are not enough places for the number of children in my area, so if they're not going 5 sessions, pre-schools won't offer a place.