I've played NL-only for 25 years and mixed for only five. I prefer an AL/NL only league for all the reason stated above, plus being in a NL-only league helps me better focus on the players on the teams in the NL who compete against my favorite team, the Cardinals. However, a couple of guys in our NL-only league whine that it's too difficult, that there too many players to keep track of. Before last season, we shrunk the rosters, deleting an OF and C position, and creating an extra UTIL position. This off-season, one owner left, and the Astros left, creating a league of eight owners with a player field of 375.

But, also being in a mixed 5x5 league of 10 owners (OBP instead of BA), gives me a chance to keep track of players in the AL, like Trout, Cabrera, and Pujols.

Obviously the more casual a fan you are the more you'll prefer a mixed league. Not everyone wants to have to know who is third in line for saves on Cleveland, or who Houston's backup C is.

We have NL and AL-only leagues with 40-man rosters, 5-12 keepers, and it's a blast. But it's a lot of work, and only four of the eight of us really put in the time to have a chance to win. I imagine that's typical of many leagues regardless of structure, but that's one point in favor of less rigorous leagues.

We have openings, BTW. Draft at Mohegan Sun, last weekend in March. New guys get $320 instead of 260 to compensate for no keepers.

I am in a 16 team mixed keeper lg and auction-base draft, with 25 roster spots; and a 20 teams mixed keeper lg with incentive-base draft order, with 35 roster spot (including 4 minor league spots). I 've participated in redraft yearly mixed lg and won 16 teams and 14 teams but choked on 10 teams league. I definitely feel what Mr Carty meant.

While myself being waiver wire shark and FAAB auction manic, draft is my weakness. The blind side of stats (or my usage of stats) led my trapped with the star due for rebound or expected raising value that never actualized. Even with mental notes of not over valuing prospects, I still tie myself with Jake McGee/Matt Moore in the past couple years.

Still, pick scrubs that stood out when your season is in rear mirror is something you can brag about in your annual fantasy league luncheon. And I enjoy picking and trading prospects for big leaguers a lot. With out -only lg, and try to find 14 or 16 reasonable men that doesn't cause saga can even be a hassle that BP may never have an article about. C'est la vie, I guess.

That's why I stick with keeper league. Seldomly a team GM can pull yearly fluke and not make you learn something from him. You want to keep Josh Hamilton for reasonable contract? Sign him to a multi years like Angels and take on the consequence later year (whether it's performance drop, or not). If your time investment not pay out for this season, in a keeper league you may collect your rewards in a couple years. It's a continuously improvement process, not one off luck or not season.

I certainly hope for analysis from BP writers for deep keeper leagues, but also realize there is a smaller market for it. At least I appreciate how expert values the gratifying effect of picking up less known player to outperform just like I do.

I have one disagreement. Leagues where players are lost/FAABed when traded from the NL to AL or vice versa are ridiculous. Why introduce something with that much luck in it.

I've played in NL only and mixed. I think the argument made in favor of NL/AL versus mixed can be addressed by the number of teams, roster size and format (re-draft, keeper, dynasty). I'm in a 16 team mixed dynasty, with 25 active and 25 reserve slots, plus 8 injured spots in season. You have to know every player and prospect on every team to have success. The more teams and/or roster spots there are, the more you have to know.

I like 14-team mixed dynasty with 40 man rosters the best. I've tried only leagues, but losing players with they are traded out of the league is too much.

How does anybody have time to play a mixed league? In an AL/NL only, you only have to be an expert on one league. I don't play roto type baseball, but I guess the answer is that mixed leagues do not go as deeply. However, that depends on how many managers there are, no? So, if you have the time to be an expert on both leagues, then a deep mixed league would have more managers to trade with.

What's really interesting is how many variations there are in leagues, just among the small group of leagues referred to in this thread. Given that,it makes the concept of dollar values and ADP very hard to pin down.
I'm in 2 (or three, depending on how you define the second) money keeper leagues. Both are auction leagues with traditional 23 man rosters. The mixed league, which has been in existence over 20 years, contains 18 teams. Along with the 23 man roster compiled through the auction and keepers, there is an up-to 17 man reserve roster, which contains anyone, major leaguers, minor leaguers, Japanese players, college players, anyone - I drafted Justin Upton when he was in high school. You keep non-major leaguers as $5 reserves until they use up their rookie eligibility in the majors. This all works pretty great. Just deep enough so we draft guys who play, as well as having people available to be picked up. The reserve draft order is based on where you finished the previous season, giving people a reason to keep paying attention. It also enables draft choices to be used in trades.
My other league is unique. Only nine owners, but each of us has an AL and an NL team. Top three in each league get paid, along with the top two combined. Only ten reserves, make the decisions there tougher and FAAB bidding exciting. If a player is traded out of a league, you keep him in the league he started in, then you can keep him in the other league the next season.
I guess there are those who find the decision over which guys getting 200 AB can be useful as an important part of fantasy baseball. I freely admit that I don't. I like having a budget to allocate in an auction and having some useful reserves to replace injured players - and there are more and more DL stints every season. Given that both of my leagues date back to the last century with remarkable stability, what we do seems to be working.