I don't know about Pidgey in bottom. I think low is more appropriate. It levels up quickly, Gust is good for the bugs and grass-types that are somewhat common early on (and the Sprout Tower but I think that's optional), it's speed (and Quick Attack) allows it to get through the 'average trainer' routes and Team Rocket grunts, at least it was when I used it (these guys will be underleveled), and it certainly isn't as bad as stuff like Ditto and Ledyba when it comes to beating the game efficiently.
That's just nitpicking though. I honestly feel that low and bottom can be made into 1 tier and I don't see much use in separating pokemon in groups of 'bad' and 'really bad'.
Anyway, Teddiursa. I did two separate ones because, like Suicune, its usefulness in Crystal and Gold is like night and day.
Teddiursa for high tier (Crystal). It isn't top because of its thin level-up movepool early on as well as the fact it is a tad annoying to catch, but putting it on your team is well worth it.
-Availability: Dark Cave, before the first gym (only in the morning though; it's somewhat rare and it likes to flee).
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Stats: Great. 80 attack before it evolves; becomes 130 when it evolves - at level 30! Solid bulk lets it take some hits and special attack is good enough to make great use of the elemental punches. Low speed but will be moving first against most average trainers because it will probably be at a higher level.
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Movepool: Level-up movepool is thin at the lower levels, though the high attack score gives Scratch a nice kick. Faint Attack will help against Morty. It's a great candidate for the easy to come by Headbutt TM, which will be OHKOing almost any average trainer's pokemon that doesn't resist it. The elemental punches will give it awesome coverage and it also learns Dig. It puts them to great use so don't worry about wasting them.
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Power: As I said, kills everything and is strong enough to work well against pretty much any gym leader battle/elite 4 battle.
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Type: One weakness. It is always a good match-up against pretty much everything. Stuff that resists normal can be covered by another move (elemental punch, etc).
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Match-ups: Only Chuck is a bad match-up. Give it the right moves depending on what your team needs, or you can just heavily damage opponents with Headbutt/Strength/Return/Slash/Thrash...
On the other hand...
Teddiursa for low tier (Gold). It comes way too late and at too low a level, though if you are willing to put in the time to training it it will make the rest of the game a lot easier.
-Availability: Around the 8th gym, and its level will be below that of your team. Takes time to train.
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Stats: See crystal analysis above.
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Movepool: See crystal analysis above.
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Power: See crystal analysis above.
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Type: See crystal analysis above.
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Match-ups: See crystal analysis above, though it can't be used for as many gyms since you will have beaten them by the time you get there. It will help against Clair with Ice Punch though and it can hold its own against Kingdra. It also does well at the elite 4.