The easiest starter is cyndiquil, no doubt. It almost makes the game too easy as long as you snag a thunder punch TM from the Goldenrod department store. It learns a variety of moves for type coverage and can quickly blitz through the game. I think doing so is kinda boring, but if you want a quick and easy win with a strong pokemon, cyndiquil is a great choice.
Totodile is very useful and can learn great physical as well as special attacks, meaning no kind of defense can stand it's power. Although there are better water types out there later in the game, if you want an aquatic buddy from the get go and more of a challenge than cyndiquil, totodile makes a good starter.
If you want more of a challenge, go with chikorita. Chikorita can be very helpful to your team with reflect and light screen and is quite sturdy. It doesn't pack quite as much of a punch as the other two starters, but can be very reliable if you need some extra turns to use potions on your other battlers. It learns poison powder early on which is very helpful. Choosing chikorita 'forces' you to raise a balanced team because of its disadvantage against most gyms, which in my opinion makes the game a longer and a more enjoyable experience.
Once you get your starter figured out, you can choose your other members. Of course this is completely up to you, but I prefer to have one pokemon of each 'basic' type (one water, grass, and fire). Something that learns electric moves can also be helpful. If you can do without not having access to fly all the time, then you shouldn't catch one of the early bird pokemon, they are pretty weak. A ground type (such as sandslash) is also quite useful. I usually buy a cubone at the goldenrod game corner because of its high defense and being able to use a ground type move early on without a TM. Once you get far in the game, if you can nab a thick club item with thief off of a wild cubone in rock tunnel and give it to yours, it's attack power in battle will sky rocket. So, thats all the advice I have to give, hope it helped you in some way.