Via Clapham Junction is simplest, though normally slower; you end at Windsor and Eton Riverside station, which is a terminus.
Clapham Junction is in two halves, with a wide footbridge that connects all the platforms. It's a bit of a walk to get from the Southampton platform (7 or possibly 9) to the Windsor platform (5 or 6), but there are lifts.
There are no engineering works scheduled on this route.
Reading station is being rebuilt, and major work is being done over Easter including Sunday 7 April, so best avoided in this instance.
The online journey planner confirms this by not showing any services via Reading that day:
http://ojp.nationalrail.co.uk/service/timesandfares/SOU/Windsor/070413/1429/dep