Review: Being a Stardust Trumpeter copy, Kaleido Ace is only something you run because you don't have any better options available. (Or out of personal preference, I too once used a Jigglypuff as a mainline attacker.) Battleraizer is where the game really gets riding for Nova Grappler.
Cardfight!! Vanguard is a game of resource preservation. When you ride from grade 0 to grade 1, you're losing a resource—one of the cards in your six-card hand—to do so. Because Battleraizer is called to the rearguard upon riding, it helps mitigate the resource loss by giving you another unit to boost with(attacking is not an option due to its low power, showing some thought on the game designers' part.) This is much like how Gigantic Charger pulls another card out of the deck to mitigate the damage calling it does to your hand, but in this case Battleraizer does so from the soul. Furthermore, Battleraizer returns to the deck after boosting, recycling its stand trigger, an invaluable asset to Nova Grappler.
While he was a rare/special in BT01, Battleraizer was made the default vanguard available in the third trial deck, and reprinted as a common in the first extra booster, making it the go-to starter for many players.
Blaujunger attains hand preservation in a different fashion. He's based in Fullbau's evolving ride, which works like this; the grade 0 unit searches out the grade 2 unit, while the grade 1 unit searches out the grade 3 unit. However, this kind of evolution ride isn't especially efficient as compared to the alternate evolution first presented by Godhawk, Ichibyoshi. The problem comes in once you hit grade 1—in order to get the grade 3, you need to call that same grade 1 unit to a rearguard circle, as well as drop a grade 3 of the same clan to search out your target card. Whereas the Ichibyoshi-style evolution simply searches out the top five cards of your deck for its target each turn in order to ride without using any cards from your hand, this Fullbau-style evolution makes you lose a card from your hand to get to grade 3. So on the turn that they reach grade 3, a player using Blaujunger will ideally have 8 cards at the end of their turn, where a player using Tsukuyomi would have 11. This is also less efficient than an old-fashioned Battleraizer ride(Battleraizer → Tough Boy → King of Sword → Asura Kaizer), where the player using Battleraizer will have 9 cards in hand while the others have 8 and 11.
Don't count Blaujunger out yet though, because there's plenty of reason to use him. To start, the Blau-series cards achieves a level of precision that Ichibyoshi imitators can't, and it comes with skills attached. With Ichibyoshi-style, you can't always find your target card in the top of the deck, so failing to ride even once will leave you nearly on the same playing field as someone using Battleraizer, and failing twice levels you completely. Blaujunger however, is much easier to achieve the grade 2 and 3 for, as you can anticipate not having a Blaupanzer in hand to ride with and therefor redraw. (Effectively searching 11 cards in the deck instead of 5.) The grade 3 is a matter of already having an abundance of G3s—already a prerequisite for any Nova Grappler deck running Asura Kaizer and/or the Death Army series—and bringing out a second Blaupanzer. Due to the precise nature of Blaujunger's deck-searching, you only need one or two Blaukruger in a deck, so it doesn't take away much space away to run and its skill unflips damage. What Blaujunger loses in resources it makes up for in security.
Admittedly, Blaujunger's final form leaves something to be desired. When compared to the likes of Mr. Invincible and Asura Kaizer, Stern Blaukruger isn't as immediately amazing. It's a self-and-column stand, which affords you a second drive check and another go at the opponent's vanguard, but it loses twin drive and costs a counterblast 2 and a drop of two Nova Grapplers from your hand to use. So on top of the Blau series leaving you with less cards than Battleraizer, this second attack (if used on the turn that Stern is ridden) takes away from your hand, leaving you with one less card than you would have had otherwise.
The solution to this is to use Blaujunger differently. The grade 3 isn't as great as the other grade 3s, so don't include Stern. Start with Blaujunger, ride Blaupanzer and add Blaukruger to your hand, on your next turn you can ride Blaukruger and focus on using a different G3. No matter what is ridden, using the model above a Blaujunger player using this method would have 9 cards in hand with their twin drive, easily leveling them with a Battleraizer player. Certain key cards Nova Grappler has access to make both Blaujunger and Battleraizer viable starting vanguards, so their use is largely a matter of personalization. Do you want greater security and deck thinning with Blaujunger, or an extra unit to start and cycling stands?
I would personally opt for the security, though obviously this doesn't preclude excluding Battleraizer from the deck, as a cycling stand is invaluable.