Well, it all depends on what your needs are. The delays in the Timefactor are better IMHO than the Kemper and there are certainly more of them. I mostly use the tape and analog delays and they are top notch. The Pitchfactor is pretty much the ultimate pitch stomp for sure. If you have to do diatonic harmonies or scalar harmonies, there is nothing better. They are both quite expensive. I have also used a Lexicon MX400 for reverbs. I'm sure the Space is just amazing judging by the TF and PF. I have heard the Modfactor was disappointing however.
That said, depending on the gig, I also use my Boss GT-100 for effects and it really plays well with the Kemper--both for changing rigs via MIDI and for effects quality. With it's programmable external footswitches and the two onboard (P.Loop & CRTL are also programmable), you can have up to 4 different effects to switch on and off. I use two for leads and two for effects and probably have around 40 presets. It's very nice. I'm actually really impressed with the quality of effects in the Boss, even coming from the Eventide stuff. The modulations, delays, reverbs, even the pitch are all very good. I would actually give them a 9 out of 10 compared to 10 out of 10 for the Eventide/Lexicon.
I actually don't use any of the effects on the Kemper, since it's easier for me to think of it as an amp replacement instead of an all-in-one box. Maybe if the footswitch came out I might change my mind but, with the crazy amount of effects and lead switching I need to do, the Kemper sounds great as an "amp" and the Boss/Eventide sound great for effects.
I'm in a Classic Rock/Hard Rock cover band and there is a lot of pitch and harmony stuff I have to cover, not to mention other effects. I'm coming from using a Marshall JVM410 previously. I could never turn it up past 2.5 and we use IEM anyway so, I figured the Kemper would be worthwhile and so far, it has!
J