Wallaby is correct about the Tom Thumb. It is an unbalanced bit and can be pretty harsh, there are many shanked bits that would be a better choice when and if the time comes for one. A well trained horse really never needs to be out of the snaffle except for specific training or disciplines.
I personally do NOT like single-joint bits. They have a crackerjack action on the horse's tongue and bars, protrude up into the horse's palate, and do not have full-mouth contact. I much prefer double-jointed bits.
Here's what I like to start youngsters in:
Full Cheek French Link. The full cheek part of it will prevent the bit from being pulled through the horse's mouth, which is big for a youngster, epecially if you lunge or ground-drive with a bit. The full cheek also applies lateral pressure, that is, when you pull on the right rein, the left cheekpiece will push against the left cheek, encouraging the horse to follow the right rein. The french link mouth is a nice double-joint bit that allows full mouth contact. There is no crackerjack action, and the bit lies nicely on the tongue.
---> A great analogy for choosing a bit mouthpiece!! Think of the bit as a bucket handle. If you had to carry a full bucket of water with that bit as the handle, would it hurt your hands? A single joint bit would pinch your hand, and you'd only really feel contact on the outside of your hand. A double joint would not, it would give you full contact, dispersing the pressure. You can think of this with many types of bits, for example: Twisted wire: ouch!! Double twisted wire: even more ouch!! Corkscrew: not as bad, but still ouch!! Slow twist: woud definitely not be pleasant!
I would use a snaffle as its the kindest bit .. but that all depends on how your horse is .. if he's extremely strong than you would oppt for a stronger bit.
And no the top one is a pelham. Tom thumbs are pretty good as you have alot more control steering and stopping. But as I said it depends on your horses temperment.
Sorry, have to disagree - I do not like tom thumbs at all. They are a shanked bit (therefore leverage), and are a single-joint bit, which I do not like at all. They do not provide a clear signal. The curb also picks up very quickly, without much warning. Although shanked bits CAN be used safely with a direct rein without damage to a horse, that is best left to professionals, as it is severe if you don't have good hands. Sorry, will add more later.
ETA - no, the top bit (dark picture) is a tom thumb, not a pelham.