We decided toddler beds are a huge waste of money (for us) and got bunkable twin beds. We sprang for nice ones (solid maple) because I want them to hold up really well over the years and eventually be furniture that dh and I will still want to have around (e.g., in a guest room) after the kids are gone. Also, the non-toxic aspect was important to me (i.e., no laminates). They look great as twin beds - not all bunkable twins do, in case you go that route. This way we can even leave them as twin beds forever if we want.
We switched them into "big boy and big girl" beds in late August (so they were 2 yrs. 3 mos. old). I actually find them FAR safer than toddler beds... those skimpy built in rails on *some* toddler beds (the ones we had available to us in stores around here) wouldn't hold dd and ds if they tried and they only go like halfway down the beds. Plus, I couldn't find any that were solid wood - no plastics, laminates, toxic off-gassing, etc.
We bought the greatest bed rails... made by Regalo they leave only a small space on either end - definitely not enough to fall out of. They also tilt down to make bed changes easy. They are soft mesh so dd and ds, who until recently still could be found pressed up against the safety rails, won't get hurt by hard plastic or wood or anything.http://www.pricegrabber.com/search_g...h=bed%2520rail
For us, the final decision was that we don't have a large house but DO have lots of relatives who love to come and visit. With just one "real" guest bedroom with a queen bed in it, we wanted the additional flexibility of being able to put 2 people in the kids' room while dd and ds sleep in our room slumber-party style
in sleeping bags on the floor.
The switch to big kids beds (again, in their own room - but adjacent to ours about 10 feet away... small houses are great in this way!!) went smoothly for bedtime and less so for naps. At first they didn't get out of bed at all, but within 2 or 3 weeks, soon they were bouncing in and out like two kangaroos at naptime, even when I knew they were exhausted. We cracked down (gently of course) and now they go right down for naps as well.