As the 2018 season heads into its last lap, there are still plenty of things to ponder in the prospect world. Who will get called up when rosters expand in September is a popular topic. Which former prospects are in contention for the Rookie of the Year Awards is another one.

Beyond that, we're excitedly anticipating our Prospect Team of the Year coming once the Minor League season has ended, and we can't wait to see who gets sent to this year's Arizona Fall League.

This week's Inbox deals with the first two questions, along with the ranking of an underappreciated (or at least underranked) group of prospects.

It's amazing that this is a debate, isn't it, given that Ronald Acuna Jr. missed a chunk of the season with a knee injury and Juan Soto began the year in A ball? Yet here we are, with the two very young, very talented outfielders seemingly the clear front-runners for the National League Rookie of the Year Award. (Cardinals starter Jack Flaherty or Phillies closer Seranthony Dominguez might beg to differ, but I digress.)

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With a month and a half of baseball still to play, it's very much up for grabs. But for the sake of argument, let's work under the assumption both will be healthy and in the lineup for the rest of the season.

The pair is currently first and second among all NL rookies in OPS, with Soto (.970) holding the edge over Acuna (.922). Acuna has the home run edge and more stolen bases, but Soto's on-base skills are superior. It's a coin flip for me for the hardware, but I'll say that if Acuna is back playing sooner rather than later, he gets the nod.

They both have tremendous upsides, so picking one for that part of the question is like deciding between ice cream or cake. But again, I'll give Acuna the slight ceiling edge. He is a true five-tool player, with his speed, while Soto doesn't bring that to the table. That said, because of his plate discipline, Soto would win the "highest floor" debate.

We talked about whether Vladimir Guerrero Jr. would get called up on this week's Pipeline Podcast. Basically, we are in the "Wait 'til next year" camp when it comes to his big league debut.

There's really no reason for Guerrero Jr. to get called up in September. The Blue Jays aren't competing, so other than to make a splash, there isn't a compelling argument to be made here. As among those who cover, and love, the Arizona Fall League, however, we here at MLB Pipeline strongly endorse letting Vlad Jr. make up for lost at-bats from that knee injury in the AFL.

As for the other top prospects listed, it's mostly splitting hairs arguing over who comes up first. The regular season for both Francisco Mejia in the Pacific Coast League and Victor Robles in the International League ends on Labor Day (Monday, Sept. 3). The things that can be considered:

1. Is the player on a 40-man roster and/or already has his service time clock going? (Mejia and Robles are a yes)

2. Is the big league team in contention? (Padres no, Nationals … maybe?)

3. Is the Minor League team the player is currently on headed to the playoffs? (Mejia yes, Robles no).

That last question isn't of the utmost importance if the answer to No. 2 is yes. But since the Padres aren't competing, but Triple-A El Paso is winning its division, I could see San Diego waiting to bring Mejia up until that run is over. Conversely, Robles' Syracuse squad is in last place, so why wouldn't the Nats bring him up on Sept. 1, or the 4th, after the IL season is over? So I'd flip the order and say Robles makes it up a little bit ahead of Mejia and we see Vlad Jr. after whenever the Super Two deadline passes during the 2019 season. 

We've talked about this now and again internally, about whether we should add a Top 10 reliever list to our top prospects by position selections. Evaluating relievers in terms of their prospect status is tough, so we haven't done it, though we do now include a reliever in our Prospect Team of the Week feature.

I was hoping that would give me some guidance, but it turns out we have chosen a different reliever every week. One of the things that makes this tough is that often a reliever can have a very good season in the Minors statistically, but doesn't necessarily have the stuff to make him a very good big league relief prospect. Using players currently on team Top 30 lists, I put together a top five. I didn't use graduated relievers like the Phils' Dominguez, who undoubtedly would make it otherwise.

1. C.D. Pelham, LHP, Rangers' No. 16 prospect: The lefty Futures Gamer has scuffled a bit in Double-A, but he still has a .226 combined batting average against, 10.6 K/9 and 13 saves this season.

2. Ian Hamilton, RHP, White Sox No. 16 prospect: He's pitched his way to Triple-A and has a combined 1.81 ERA, .220 BAA, 11.1 K/9 rate and 18 saves.

3. Durbin Feltman, RHP, Red Sox's No. 12 prospect: I could see the 2018 third-rounder topping this list soon enough. Jim Callis' pick to be the first member of the Draft class to get to the big leagues, Feltman is already in the Carolina League, has a 28/3 K/BB ratio and a .167 BAA in 16 innings.

4. Jimmie Sherfy, RHP, D-backs' No. 13 prospect: He's tasted the big leagues the past two seasons and really has nothing else to prove. This year in hitter-friendly Reno, he has a 1.45 ERA, .190 BAA, 14 saves and an 11.8 K/9 rate.

5. The Burdi brothers: Nick is the older one and is the Pirates' No. 20 prospect after they took him in the Rule 5 Draft last December. Zack is No. 17 on the White Sox list. Both are back on the mound after undergoing Tommy John surgery in 2017. Both have big-time power stuff and closer potential.

Beyond this five, I also really like Cody Carroll, now an Oriole, and keep an eye on D-backs reliever Yoan Lopez, who is really figuring things out.