Holly!
or Lewis!
But you can't have either of them!
In reality I wouldn't worry too much about the breed, let your mom choose since she wants it to be her dog and then work with whatever you get.
I did not pick any of our dogs and I'm now competing in agility, rally-o and obedience with both Holly and Lewis (I'm sure Skye would absolutely love agility and would be really good, but she is my mums and I said I would refrain from training her).
Holly needs one more certificate to get her Advanced Rally-o title and Lewis needs one more Novice certificate to get his title (he's only been to one show so far as well). At the Rally-o show one of the judges was so impressed with Lewis that she said I should do obedience with him, I told her I have been for the last couple of months
.
Holly has CGC foundation and bronze so far. And as you probably know, Holly can do a lot of tricks. Lewis can do a couple (I haven't tried to teach him many though - he can spin, shake paw and jump through my arms).
We are doing an agility champ show this weekend (Lewis' first). Holly will start entering AD events soon too. I seem to be known as the person with "that really fast little dog" at agility, she can get a faster time than a lot of dogs much bigger than her if she goes clear and it's the right course (she can do tighter turns than larger dogs).
Lewis just started agility class about a month ago but he can do weaves and is improving in all areas really quickly.
Lewis hasn't entered an obedience comp yet, but when he does I expect him to do well. Holly is very close to advancing from Special Beginners to Novice, she's had the required score a couple of times but there was a German Shep with a higher score
so she came second
. She can do all the required tasks up to Test C and CD level (heel on/off lead, straight recall, retrieve, scent discrimination, send aways, recall to heel position, down on recall, stand for temperament test, 5 minute out of sight stay, down-stay, sit-stay, stand-stay - I've probably forgotten some stuff).
And as an added bonus...... Holly has just started a new sport!....... weight pull!
Holly has great potential in that sport too. She had her first try last weekend.
So....
Holly = PugX, 6.7kgs
Lewis = Pomeranian(?), 5.7kgs
Both are small dogs, neither were selected for potential sporting ability/intelligence (there breeds were not really considered at all actually). I didn't get Lewis until he was 3 1/2 and he came with a few behavioural issues (they are much better, but still there, especially the not liking strangers bit), I've had him 18 months.
Both are doing more than most dogs in our club, including all the Border Collies!
So either I got incredibly lucky to end up with two super smart small dogs of completely different breeds.... or it really isn't just about the breed....
But, to increase your chances of getting a dog to do sports with I would suggest not getting a terrier. Terriers can be very independent, I don't see them in any of our sports much. Although they could do them, they have the intelligence and energy, they would need a lot of time and patience. Also, I'm not sure terriers are all that cuddly.
The top small breeds that I would suggest if you really want the sporting ability would be:
Papillion
Poodle
Spaniel/PoodleX
Bichon
Shih Tzu
But I really do think that almost any breed would be fine. I would focus on what kind of dog I wanted at home rather than what it will be like at sports as the dog will spend most of it's time being a pet and only a few hours a week being a sports dog.