CL is more prestigious, but the EPL is much more difficult.
The false notion that the CL is the true proving ground for players to see if they cut it at the "highest level" just seemed silly to me, because when you look at it realistically it is far from anywhere close to being a barometer for quality. In the EPL each and every season you know you will have to play Tottenham, Chelsea, Arsenal, Liverpool, MU, and MC twice so those are 10 insanely difficult matches you have to play in if your on one of those teams. Where as in the CL, in the group stages you end up with 1 very good team and sometimes potentially a 2nd good team if you are in a Group of Death. So for the majority of the teams they end up having to to play 2 matches of real quality and the rest are 2nd tier matches. Once in the knockouts you again either end up with a very good team or another 2nd tier team and it goes like that until the SF's and Final. You simply don't compete regularly enough with top teams in the CL for it to be some sort of barometer.
In the best case scenario of a team facing very good teams in the CL from start to actually winning the CL it would be a maximum of 6 teams(2 in GS, 1 R16, 1 QF, 1 SF, 1 Final) in the worse case scenario it would be 2 teams(0 in GS, 0 R16, 0 QF, 1 SF, 1 Final) similarly to Monaco last season had they beaten Juventus. For the very large majority of teams bar the elite 3 to 5 teams through the CL campaign you end up playing 2 or 3 very good teams on averages one in the GS and one or two in the Knockouts. So when you compare those two it is quite evident that your going to face more competitive teams in the EPL in a season of football.
No offense, but look at United's CL campaign it might as well have been the Europa League campaign. The group was none existent and the R16 tie is basically another EL knockout round.