We happened to get a convertible because we liked the looks as a crib, but I don't think they're necessarily for everyone. If your kid is a chewer, are you going to want a bed with a tooth-marked foot board? We already had a twin and never bothered to convert the crib to a toddler bed (you have to buy a separate conversion kit, anyway), so we went straight from crib to twin. You don't need a convertible for that. I'm not sure we'll even use the full-size bed frame down the road.
My advice is look for a style that makes you happy. If you end up without a convertible, there are plenty of options as your baby grows. If you do end up with a convertible, there's nothing that says you HAVE to use it as a toddler bed and full-size frame eventually but you'll still be able to consider whether you want to use those options.
Re: convertible vs plain old crib
We happened to get a convertible because we liked the looks as a crib, but I don't think they're necessarily for everyone. If your kid is a chewer, are you going to want a bed with a tooth-marked foot board? We already had a twin and never bothered to convert the crib to a toddler bed (you have to buy a separate conversion kit, anyway), so we went straight from crib to twin. You don't need a convertible for that. I'm not sure we'll even use the full-size bed frame down the road.
My advice is look for a style that makes you happy. If you end up without a convertible, there are plenty of options as your baby grows. If you do end up with a convertible, there's nothing that says you HAVE to use it as a toddler bed and full-size frame eventually but you'll still be able to consider whether you want to use those options.