I've had an Altitude for 2 riding seasons and I can't say enough good things about it. I've ridden the Thunderbolt as well. I like them both. The Altitude is a little slower on the grinding uphill climbs-but all the 6" bikes are a little bit slower on the long climbs. For smooth climbs and dirt roads I use the shock platform (it helps a lot). For the really chunky, ledgey climbs, the Altitude seems to shine. It just eats bumps. I think the Altitude is better when going fast in the chunder on the way down, and it makes for a fun day in the bike park. I'm comfortable taking it anywhere and not being worried if I have 'enough' bike. It is a really, really versatile bike.
The flip side of that is that the Thunderbolt is also a great bike but it has a slightly narrower focus. It climbs fast and rips the flowy downhill. I have only ridden it locally (not tested in Moab or anything like that), but I came away impressed. I ride all over Colorado, as well as several trips each year to Moab and Sedona, as well as a couple of bike park days each season and I haven't found much the Altitude can't handle.
If I could only have one bike for all of these trips, it would be the Altitude (which is what I have). However, if I wasn't hitting the seriously steep stuff, or if I was not looking specifically for a 6" travel bike, I'd go with the Thunderbolt. And coming from your HT, the Thunderbolt will probably seem like a huge bike anyway.
To address your original post more directly, yes, the Altitude is more of a handful to get to the top but I think it is worth it for where I live. Your profile lists you as from Bend. There is some rowdy stuff up there. If you like hitting the bigger stuff, go with the Altitude. If you are more of a ripping the buff singletrack where you are spinning the pedals as fast as you can for the whole ride, try the Thunderbolt.
