Blastoise vs Swampert
Blastoise and Swampert don't seem to have much in common at first glance, but a deeper look can prove that assumption to be quite untrue.
First, they're both Water Starters.
Second, they both appear in parallel running games. In fact, they were both the Water Starter choices within the same generation.
Third, they're both primarily defensive Water Pokemon. With fantastic bulk and good support movepools, these two Pokemon help define the term "Bulky Water". Sure, both have their niches in competitive battling (Blastoise is a Rapid Spinner while Swampert is a Stealth Rock lead) but even then, bulk plays a major part in their battling capacity.
It's interesting to note that in a battle, these two Pokemon are quite evenly matched. Moreso than any other Starter, I'd wager. I mean, Blastoise can hit Swampert with STAB Hydro Pump (coming off an average Sp. Atk and hitting an average Sp. Def) for neutral damage but Swampert can hit back with neutral STAB Earthquake (coming off a great Atk but hitting a great Def) so the victor is actually not that clear cut.
Which one of these Pokemon do you prefer?
Which one would win in a battle?
Which one is more useful overall?
Personally, I'm going to go for Blastoise. I've always loved that Pokemon and turtle + cannons is an epic win right there. Swampert gave me a bad first impression (I literally thought it was just an odd looking Mudkip) and doesn't seem quite as creative as it's counterparts Sceptile and Blaziken. So, Blastoise it is for me (though Swampert is the most useful overall)
Other Blastoise Starter matchups:
Blastoise vs Feraligatr
Blastoise vs Empoleon
Blastoise vs Daikenki
Other Swampert Starter matchups:
Feraligatr vs Swampert
Swampert vs Empoleon
Swampert vs Daikenki