My vote goes to 170" 4x4 (which comes as a high roof). Truly I think you'll kick yourself for getting a 144" wb sprinter, with (potentially) two small kids and the idea that you're going to pack bikes and a bike trailer. I don't see it working out well. You'll have a pretty big van that isn't really that comfortable for a family. If you're dead set on a 144, get a high roof. There is some 11" height different between low and high roof, and a penthouse is likely going to add 6"+ anyway so you're not saving much in terms of height and handling, and I'd venture to guess the penthouse is heavier. Plus you have the extra expense, poor insulation factor, no stealth, tiny bed, weak lifting mechanisms that get stuck (think about lifting and closing with a snow load). Stand up room in all weather, all the time is amazing. I still find myself stepping in and hunching over for a few minutes before I realize that I can stand up and move around freely. Plus I'll have cabinets up high for some light weight items, food etc.
I have two toddlers myself (18 months and just over 3 years old), sold my EB E350 4x4 for a new Sprinter 2500 170" 4x4. I'm JUST starting the interior
build process but have about 5000 miles on the van so far. I haven't driven a 144" sprinter but I can tell you that the 170" drives great. In fact I'd say it gets around parking lots as well as my Ford E350 did on 35s, despite the much longer wheel base. The front wheels turn to a very sharp angle which easily drags it around corners. I've talked to others who thought they just couldn't stand the 170" wb on a daily driver but I've been daily driving mine, even around downtown Portland. I honestly do not find it to be an issue at all. The wheelbase is similar to a Ford super duty crew cab long bed, but the turning radius is much much better.
I'm building my van with a walk through floor plan, seating for four (four forward facing seats, driver and pax swivel, rear seats have foot-rests and latch anchors), 3' galley cabinets on each side, a raised bed to sleep sideways 60" x 74" (look up flarespace.com), or front-back up to 7' long with another bed panel. A dinette halfway under the raised bed that will make into a 4'x5'10" bed for the kids. And 3' x 3' x 5'10" storage area in back for bikes and toys. Yes I'll have to remove front wheels but the bikes will be secure and dry. On the sliding door and opposite I have CRL windows with awning style openings (can be open in the rain), a small slider in each of the rear flarespace panels, and two fantastic fans on the roof. This will allow the car seats to remain mounted all the time, it is no fun having to remove and store them (often outside) to make a kid's bed every night. The front seats can all be open for sitting, while both beds are made or occupied, and standing room in the galley area. I know that isn't a very good description, I have it marked out in my van with tape and such but not drawn up.
One of the big things we struggled with on our last truck and four wheel camper, and a sportsmobile EB-51 that we rented was having to re-configure the interior any time we moved, or not have sitting space while someone else is sleeping. With two kids, I don't want everyone to have to get up just because one person is up. Additionally, having to re-configure and pack away beds just to sit down or move around gets really annoying to us. Where do the kids go when you shuffle and reconfigure everything and it's 40 degrees and raining outside? Is the car seat soaked in water? Where are I going to store all of this bedding when everything is closed up? Man I hate setting up the car seat every day. lol
My feeling about being really open (ie penthouse) is that it is nice when the weather is just right, but generally if I want to be outside in open air, I'll just be outside. Otherwise, I want peace and quiet and to be able to keep it dark. You know how it can be with kids, sometimes you want to be able to control their environment better for your own sanity. Don't forget that you can buy screen kits for the huge rear door and sliding door openings too. One thing I love about the high roof is that the doors open all the way to the top, so it really opens up. You could also use the dometic/seitz acrylic type windows that fully open if you want to have more fresh air, heki skylight etc.
I planned to install a penthouse on my Ford 4x4 van. I insulated and made a basic interior, four captains chairs and used it a bit. Somehow I was thinking the trade off of having the shorter wheel base and pop-top would be totally worth it, but every time I got in a high top I was just blown away with how comfortable it was and how open and roomy it felt. Since driving the sprinter, the ONLY time I've wished for the Ford again was trying to pull into some of the coffee shops with low overhangs! ZERO complaints about the wheelbase and driving it around town. REALLY. If you can comfortably drive a 144" high roof the 170" should not be a problem either. It's in your head.
Mocking things up. 10' behind the back of the head rest to the center of the rear doors with the seats in this position. Plenty of room to step in, plenty of room to walk in between the seats. Plenty of room to sit and drink beer (and access the fridge/galley) while the little ones are sleeping in back.
Untitled by
Brian Wilson, on Flickr