I've had three (currently got the third).
My first was a 3.5T in virtually mint condition. I can't remember what I was saving for but I sold that one to Urban. My second was a 2.8e which was a lot heavier but the lenses were beautiful. Again, it went as part of a trade. My current one is another 3.5T - this time grey. Not in as good condition as the first but available at a price I couldn't ignore. I'm thinking about getting it overhauled as it isn't as silky smooth operator as my first - but I'll wait until I get a couple of rolls through it.
Personally, I reckon the 3.5T is probably the best bang-for-buck Rolleiflex as the lenses are first rate - not quite up there with the 2.8 Xenotar and Planar versions, but extremely good. The 3.5T also accepts Bay 1 accessories which tend to be a fair bit cheaper than the 3.5F (Bay 2) and 2.8 series (Bay 1).
I can see me keeping this a good while as it's not an expensive / collector's piece but there's always the issue of having a fixed focal length lens compared to a 'Blad. This time round, I've got some close-up lenses (Rolleiparkeil) for when I want to focus a bit closer.
For some, Rolleis can be a bit "Marmite" but, when you see what can be achieved by the likes of Vivian Maier, Avedon, Bailey and a host of others, you can see why they remain extremely popular and tend to hold their value well when in good condition.