we have an adjustable based cot, used from birth till baby is 18mths now. we have lowered the base 3 times already, last notch now, but it's a huge pain to pat her and put her to sleep when the bed is so low. don't really have a choice i guess, but i think the adjustable thing worked for us, since i didn't have to worry about the bending down until now.
our cot also converts to a toddler bed, not sure when we'll switch, i'm looking forward to it tho, as putting her down is not that much fun now, with the height of the base.
btw, we've tried a cot with adjustable side on vacation, works reasonably well, but i worry about too many parts on the side that might be dangerous to the baby, especially as she starts figuring out how to work the knobs.