Since you don't actually need the service as day care . . . but are looking for socialization for her, I think 2-3 is a fine age to begin. However, you've named the two most expensive options: Mont. and Primrose. Before you make a decision, look around at all your options. Don't get too caught up in "curriculum". At that age, they're finger painting and talking about the color yellow. For those concepts, a licensed teacher doesn't have a whole lot more to offer than the enthusiastic high-school grad with creative ideas. The "teacher" whom I liked best when my girls were in day care was a high school grad + a CNA; she had no formal training in early childhood education.
I'd look for something along the lines of a Mother's Morning Out at a church. These tend to be 2-3 days a week, mornings only. In your shoes, I'd vote for a half-day program to allow her to ease into the concept. These programs are also considerably cheaper than full-time day care. My girls always enjoyed /remembered most "themed weeks", so I'd say look for a program that plans in that way. That is, the lead teachers says (in summer), this week will be water week -- bring bathing suits, and we'll be playing in the sprinkler and playing beach ball games. Next week will be animal week, bring your favorite stuffed animal, or it's apple week -- we're going to draw pictures of apple trees, eat green and red apples, count seeds in the apples and plant the seeds in cups.
If I were you, I'd avoid an at-home day care. I'm not saying they're bad -- not at all -- but in such a set-up you're going to get a smaller group, and your daughter is likely to spend her time with younger /older children. For your goals -- socialization and familiarization with group behavior -- she'd be better off in a small class of all 2-year olds.
Once she starts, ask her lots of questions about whether she's making friends, whether she's enjoying herself, etc. She's old enough /verbal enough to tell you. If you're not satisfied, if your goals aren't being met, keep looking.
Consider, too, that you could meet these same goals though swim lessons, gymnastic lessons, or day camp next summer, all options which are available for 2-3 year olds. Though that wouldn't provide your wife with any time for working alone.
